Fireballs and Meteorites - SOTT.NET: July 2008

California, US: Mystery fireball streaks across sky

Richard Winton
Los Angeles Times
Tue, 01 Jul 2008 19:50 EDT

Witnesses across Southern California say they saw an object 'moving very fast across the northern sky' and falling near the San Bernardino Mountains. Officials have no firm answers on what it was.

©LA Times

From Hollywood Hills to the Nevada state line, people reported seeing a fireball streaking across the sky and falling near the San Bernardino Mountains this morning. But explanations of the mysterious object were scarce.

San Bernardino County Fire Dispatch reported receiving dozens of calls related to what was described as fireball moving at high speed and falling in northwest sky around 10:40 a.m.

"We got quite a few reports. It started with a gentlemen in the Lake Arrowhead reporting a fireball in the Meadow Bay area and then we started getting calls from all over," said San Bernardino County dispatch supervisor Tom Barnes. "Fire crews in Barstow and on I-15 near Stateline came up on the radio and reported an object in the sky moving very fast across the northern sky and described it as yellowish green in color with streaks of debris. It looked like it burned up before it hit the ground."

Barnes said the department has "basically determined it was most likely not an aircraft and was probably man-made or a meteor entering the Earth's atmosphere."

Meteors and meteorities are small rocky fragments of other planetary bodies that fall to Earth. A fireball is one of a most common class of meteor, named because they are bright, streaming orbs. They decelerate from 60,000 mph to 200 mph and often fall to earth or don't survive the journey.

Some very bright fireballs can be seen in the day, experts say. Studies have indicated that about 25 meteorities weighing more than fifth of a pound fall on an area the size of California annually. Caltech experts say about 300 to 400 larger meteorites fell in California during the last century.

John Haire, chief of media relations for Edwards Air Force Base, said the base did not conduct any tests and he knew nothing about the event. "I thinks some people have been watching too much "X-Files," he said, referring to the popular show about FBI agents investigating phenomena that had no conventional explanation.

Most of the reports were in Riverside and San Bernardino, but a few people reported seeing the fireball as far west as the Hollywood Hills.

Federal Aviation Administration spokesman Ian Gregor said the FAA had no reports of any missing or down aircraft and the military had not informed the agency of any problems with aircraft or missiles.

The Barstow Fire Protection District dispatched firefighters to near the town of Calico but found no evidence of a meteorite or anything else hitting the ground, officials said.

On rimoftheworld.net, which covers the San Bernardino mountain area, those monitoring local rescue aircraft frequencies reported hearing a fire attack plane detect an emergency beacon near Butler Peak in the Big Bear area. But no signs of any downed aircraft were found.

Earth Not Ready for Meteors or Comets

Brian Handwerk
National Geographic
Tue, 01 Jul 2008 23:23 EDT

A hundred years after a mysterious and massive explosion struck Russia, experts are warning that Earth is ill prepared to face a cosmic catastrophe that could do similar damage.

The blast, known as the Tunguska event, leveled some 770 square miles (2,000 square kilometers) of forest with the power of nearly 200 Hiroshima-size atomic bombs.

An explosion rips through the Siberian wilderness in an artist's conception. A hundred years after a mysterious blast leveled some 770 square miles (2,000 square kilometers) of forest in Siberia, experts are saying that Earth is unprepared to face a similar blast caused by a meteor strike.

Remarkably few people witnessed the event, and debate has raged for decades about its cause.

One of the leading theories is that a comet or asteroid hit Earth or exploded upon entering the atmosphere above remote western Siberia.

"Had that same object exploded over a metropolitan area, there would have been millions of people killed," U.S. Representative Dana Rohrabacher (a Republican from California) said yesterday at a briefing at the Planetary Society in Pasadena, California.

"Right now we have no plan in place to detect these objects far enough out to deflect them."

Odds Are Slim

Meteors in the form of about a hundred tons of dusty particles reach Earth every day.

In fact meteors seen on an average night or during an annual shower are mostly small particles burning up as they enter our atmosphere.

Because Earth is pelted with tiny objects all the time, assessing the probability of larger impacts is far more difficult and controversial.

Experts admit they don't yet know how many so-called Near-Earth Objects (NEOs) orbit close enough to pose a threat.

Most NEOs are asteroids, and NASA currently classifies about 959 asteroids as potentially hazardous.

To qualify, the bodies must be at least 500 feet (150 meters) wide and be capable of approaching Earth within 4.7 million miles (7.5 million kilometers).

By some accounts, the object that might have caused the Tunguska blast was not particularly large in the world of NEOs, highlighting the fact that larger objects need not hit populated areas to cause damage.

On average, mid-size meteor strikes occur once every 300 years, NASA estimates.

What's more, only a tiny fraction of Earth's surface is heavily populated, and about 70 percent is covered with water. So the odds of a direct strike on a populated area remain quite remote.

Still, meteorites that splash down in oceans can cause tsunamis. And land impacts even in remote locales can raise debris and dust that may alter climate by blocking sunlight and spawning acid rain.

"The chances are not large, but they are not zero either," said William Ailor, an NEO expert with the Aerospace Corporation, a federally funded research center in El Segundo, California.

Under the Radar

Alan W. Harris of the Space Science Institute in Boulder, Colorado, has participated in numerous studies supported by NASA to evaluate the NEO hazard.

He reported that impacts capable of causing global climate disasters that could claim a billion lives are likely to happen once every million years.

And once every billion years or so the possibility exists for a massive asteroid impact to wipe out much of the life on Earth.

Harris noted that survey work on large NEOs - those greater than 0.6 miles (a kilometer) in diameter - during the last decade has ruled out such apocalyptic events in the foreseeable future.

"The good news is we have conducted the 'Spaceguard' survey, which has detected most of these very large objects," he said.

"We think we've detected all the NEOs big enough to cause a mass extinction and pretty much eliminated that risk."

Meanwhile smaller objects that can cause significant destruction are currently flying under the radar.

That's why Rohrabacher and the Planetary Society have called for increased federal funding to find and track dangerous NEOs and develop strategies to deflect them.

"We now have the technology to prevent the next [strike]," said Ailor, the Aerospace Corporation's NEO expert. "But we have to be looking for it, and we're not looking at things that small."

Many NEO experts stress that the National Science Foundation's Arecibo Observatory in Puerto Rico is key to finding and tracking potential Earth-bound objects.

NEO hunters such as Don Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, California, say that Arecibo is critical to their work.

It's not enough to know that an asteroid is headed toward Earth, Yeomans said.

"You have to know how big it is, its shape, its mass, and its rotation characteristics," he said. "One of the very few ways you can do that is with the radio telescope techniques."

But funding cuts mean that the massive radio telescope could soon be shut down.

As for deflecting NEOs that pose a threat, most experts agree that decades of lead time will be key to dealing with the problem.

"The main risk lies with those objects that we have not even found yet," the Space Science Institute's Harris said. "So the most important thing is to continue [surveillance]."

Russian expert says nuclear devices can defend against asteroids

RIA Novosti
Tue, 01 Jul 2008 14:36 EDT

Nuclear explosive devices are the most effective means of protecting Earth from possible collisions with space bodies, including comets and asteroids, a Russian nuclear physicist told RIA Novosti on Tuesday.

Scientists around the world have long been seeking means of protecting the Earth from the threat of dangerous Near Earth Objects (NEOs). Scientists say such collisions pose a threat on average once every 200-1,000 years.

Vadim Simonenko, deputy head of the Russian Federal Nuclear Center, believes that nuclear explosive devices are more energy efficient, compact and less heavy than lasers or the so-called "gravitational tractors" in terms of their practical application as "weapons against NEOs."

"We in Russia have a wealth of experience in the controlled use of nuclear explosions for peaceful purposes," Simonenko said. "A nuclear device in skilful hands is like a scalpel in the hands of a surgeon."

The scientist said special nuclear devices must be created for effective use against NEOs. In order to disperse an asteroid with diameter of up to 100 meters, these devices must have a yield of about one megaton of TNT equivalent, and weigh several hundred kilograms.

"It is a difficult technical task but it can be accomplished. Besides, there is no need for actual testing [of these devices] because it may be done through computer modeling," he said.

Existing nuclear devices, both military and civilian, were created for specific purposes and do not meet the requirements for "precision strikes" against NEOs, especially comets, which are less predictable than asteroids, Simonenko said.

An earlier report at a Moscow scientific conference said 99942 Apophis, or Asteroid 2004 MN4, with a diameter of 350 meters, currently poses biggest space threat to Earth.

In 2029, this NEO will be at a distance of only 36,000 km (22,400 miles) - closer than satellites in geostationary orbit. Earth's gravity could alter the path of Apophis in such a way that it would collide with Earth on its next approach in 2036.

The explosion could surpass the famous Tunguska explosion of June 30, 1908, which affected a 2,150 square kilometer (830 sq miles) area of Russia felling over 80 million trees in the Krasnoyarsk Territory in Siberia.

Some researchers believe, however, that blowing up NEOs in space poses could result in large fragments surviving the fiery passage through the atmosphere and still hitting the planet.

They propose a more cautionary approach toward dealing with NEOs, by deflecting them from their collision path toward the Earth.

"Deflection is the most favorable strategy, but it requires a considerable early warning period - up to a few years," Simonenko said. "We may not have such a luxury because small asteroids [100-150 m in diameter] are hard to detect."

The Tunguska Event and the 2 million acre Metz Wildfire - Can We See a Connection? Historical Novel Suggests There Might Have Been

Press Release Newswire
Tue, 01 Jul 2008 12:16 EDT

One hundred years ago, a large asteroid or comet exploded over sparsely populated Tunguska in Siberia. Ash soared 40 miles high and spread around the world, causing atmospheric, seismic, and magnetic disturbances worldwide. A drought ensued in northern Michigan that led to a devastating two-million-acre wildfire. The historical novel "Devil in the North Woods" suggests a possible connection between these events.

Lake Linden, MI -- July 1, 2008 -- You may have heard of the June 30, 1908, explosive event that took place over Tunguska in the remote interior of Siberia. But have you heard about the two-million-acre wildfire that incinerated that huge chunk of northeastern Michigan's farm and timber land in October of 1908? A century later, does the evidence indicate a possible connection?

In the prologue of the 2005 historical novel "Devil in the North Woods," author Walt Shiel suggests just that:

The Sky Splits Apart

On June 30, 1908, a 100,000-ton meteorite or comet plunged to Earth above the sparsely populated tundra of Siberia. Angled 30 degrees to the horizon, it ripped through the atmosphere from southeast to northwest at 50 times the speed of sound and exploded four miles above the ground with the force of a 40-megaton nuclear bomb. Ash and pulverized debris soared 40 miles high and spread around the world, causing brilliant sunsets and sunrises as far away as Western Europe, glowing night skies bright enough to read by over much of the Earth, and seismic and magnetic perturbations 2500 miles from the explosion's epicenter.

A month later in North America, following an early wet spring, northern Michigan plunged into an extended drought that left the dense underbrush in the virgin forests dry, brittle, and flammable, perfect conditions for a rash of forest fires.

Was the extraterrestrial visitor connected to the Michigan drought and wildfires? We will never know for sure, but we do know that Michigan's weather that fall took a sudden, unexpected shift.

On this 100th anniversary of the Tunguska event, we should remember that is the only event of its kind in human history for which we have recorded eyewitness accounts. As Don Yeomans, manager of the Near-Earth Object Office at NASA's Jet Propulsion Laboratory, says: "On average, a Tunguska-sized asteroid will enter Earth's atmosphere once every 300 years.

Comment: Now, remember that's an average.

And, 100 years after the Metz, Michigan, wildfire, we are all watching the wildfires raging through northern California. "Devil in the North Woods" tells the true story of the Metz fire and how the farmers, loggers, and merchants fought to survive without the benefits of advance warnings or modern firefighting equipment.

The Midwest Book Review said that Shiel's book "vividly recreates the terrible blaze from start to finish, the toll it took, and the trials of human beings forced to recover from the devastating losses it inflicted. Through telling the story of man vs. nature, its core is emotional and human-centered." And the Historical Novel Society noted that the "compassionate writing creates a community of bright, supportive, and determined people, whose characters develop and deepen as the fire grows."

Walt Shiel has been freelancing for magazines in the U.S. and abroad for two decades and has written four books, including "Devil in the North Woods," two military history books, and a collection of short stories.

Life Altered 12, 900 Years Ago By A Giant Comet?

Science Daily
Wed, 02 Jul 2008 16:52 EDT

Geological evidence found in Ohio and Indiana in recent weeks is strengthening the case to attribute what happened 12,900 years ago in North America -- when the end of the last Ice Age unexpectedly turned into a phase of extinction for animals and humans - to a cataclysmic comet or asteroid explosion over top of Canada.

A comet/asteroid theory advanced by Arizona-based geophysicist Allen West in the past two years says that an object from space exploded just above the earth's surface at that time over modern-day Canada, sparking a massive shock wave and heat-generating event that set large parts of the northern hemisphere ablaze, setting the stage for the extinctions.

©University of Cincinnati

Ken Tankersley.

Now University of Cincinnati Assistant Professor of Anthropology Ken Tankersley, working in conjunction with Allen West and Indiana Geological Society Research Scientist Nelson R. Schaffer, has verified evidence from sites in Ohio and Indiana - including, locally, Hamilton and Clermont counties in Ohio and Brown County in Indiana - that offers the strongest support yet for the exploding comet/asteroid theory.

Samples of diamonds, gold and silver that have been found in the region have been conclusively sourced through X-ray diffractometry in the lab of UC Professor of Geology Warren Huff back to the diamond fields region of Canada.

The only plausible scenario available now for explaining their presence this far south is the kind of cataclysmic explosive event described by West's theory. "We believe this is the strongest evidence yet indicating a comet impact in that time period," says Tankersley.

Ironically, Tankersley had gone into the field with West believing he might be able to disprove West's theory.

Tankersley was familiar through years of work in this area with the diamonds, gold and silver deposits, which at one point could be found in such abundance in this region that the Hopewell Indians who lived here about 2,000 years ago engaged in trade in these items.

Prevailing thought said that these deposits, which are found at a soil depth consistent with the time frame of the comet/asteroid event, had been brought south from the Great Lakes region by glaciers.

"My smoking gun to disprove (West) was going to be the gold, silver and diamonds," Tankersley says. "But what I didn't know at that point was a conclusion he had reached that he had not yet made public - that the likely point of impact for the comet wasn't just anywhere over Canada, but located over Canada's diamond-bearing fields. Instead of becoming the basis for rejecting his hypothesis, these items became the very best evidence to support it."

Additional sourcing work is being done at the sites looking for iridium, micro-meteorites and nano-diamonds that bear the markers of the diamond-field region, which also should have been blasted by the impact into this region.

Much of the work is being done in Sheriden Cave in north-central Ohio's Wyandot County, a rich repository of material dating back to the Ice Age.

Tankersley first came into contact with West and Schaffer when they were invited guests for interdisciplinary colloquia presented by UC's Department of Geology this spring.

West presented on his theory that a large comet or asteroid, believed to be more than a mile in diameter, exploded just above the earth at a time when the last Ice Age appeared to be drawing to a close.

The timing attached to this theory of about 12,900 years ago is consistent with the known disappearances in North America of the wooly mammoth population and the first distinct human society to inhabit the continent, known as the Clovis civilization. At that time, climatic history suggests the Ice Age should have been drawing to a close, but a rapid change known as the Younger Dryas event, instead ushered in another 1,300 years of glacial conditions. A cataclysmic explosion consistent with West's theory would have the potential to create the kind of atmospheric turmoil necessary to produce such conditions.

"The kind of evidence we are finding does suggest that climate change at the end of the last Ice Age was the result of a catastrophic event," Tankersley says.

Currently, Tankersley can be seen in a new documentary airing on the National Geographic channel. The film "Asteroids" is part of that network's "Naked Science" series.

The new discoveries made working with West and Schaffer will be incorporated into two more specials that Tankersley is currently involved with - one for the PBS series "Nova" and a second for the History Channel that will be filming Tankersley and his UC students in the field this summer. Another documentary, this one being produced by the Discovery Channel and the British public television network Channel 4, will also be following Tankersley and his students later this summer.

As more data continues to be compiled, Tankersley, West and Schaffer will be publishing about this newest twist in the search to explain the history of our planet and its climate.

Climate change is a favorite topic for Tankersley. "The ultimate importance of this kind of work is showing that we can't control everything," he says. "Our planet has been hit by asteroids many times throughout its history, and when that happens, it does produce climate change."

Adapted from materials provided by University of Cincinnati.

Tanzania holds meteorite with clues on solar system birth

Lucas Lukumbo
Sunday Observer
Sun, 29 Jun 2008 03:56 EDT

A Tanzanian renowned physicist cum astronomer, Dr Noorali Jiwaji has challenged the government to work out modalities for scientific study of a rare type of meteorite which scientists say landed in Tanzania in 1938.

Dr Noorali Jiwaji who is a Lecturer in Physics and Head of Department of ICT in the Faculty of Science Technology and Environmental Studies at the Open University of Tanzania (OUT) has said Tanzania has competent chemists, biochemists and geologists to undertake the research.

He was responding to questions from this reporter in an exclusive interview on the a rare type of meteorite, labeled Ivuna meteorite, which scientists say could hold clues to the birth of our solar system.

''The meteorite has a knowledge value. We could understand the process by which the solar system was formed, including the initiation of life.

It has been found to contain some amino acids, the building blocks from which living things are made,'' he said.

He said the fact that Ivuna meteorite was found in the 1938 and was well preserved to prevent deterioration for the past two or three decades, our own samples also need to be preserved to enable future scientific research.

Dr Jiwaji also called for Tanzania to use astronomy as a tourist attraction saying that Tanzania has unique skyline.

''We are at the equator where you can see almost all the stars, and we have no light pollution.

We have dark skies where numerous stars are vividly seen unlike in many developed countries where the skies are extremely polluted by the bright lights that leaks upward into space,'' he stressed adding, ''we could train star tour guides to cater for the astronomy tourism.''

According to the expert, meteorites are bodies that fall on earth from space. They originate from the asteroid belt between the orbit of Mars and Jupiter.

There are millions of pieces around the sun in the area and that due to gravitational pull of the planets, once in a while are attracted towards the earth.

He said 200 tons of material falls on to the earth each day from space, most of it in the form of small particles or dust.

Most of this material burns up when heated by friction with the thick atmosphere that surrounds us. Shooting stars that we see during the night are best example of such burning bodies.

Large bodies however do not burn up completely and fall to earth as meteorites.

The Mbozi meteorite near Mbeya in Southern Tanzania is a huge piece of mainly iron weighing 16 tonnes is among the top ten largest meteorites to fall on earth.

The largest is the Hoba meteorite in Namibia weighing nearly 70 tonnes.

The Ivuna meteorite is a typical example of meteorites originating in the primordial material from the outer fringes of our solar system, and from which the sun and the solar system have formed.

The material of the sun is composed of hydrogen, helium and interstellar (between stars) dust.

When the primordial material from the edge of our solar system nears earth it is sometimes seen as comets with long tails formed by its dust pushed away by sunlight.

The Ivuna meteorite is one such piece that was trapped by the earth's pull and fell near Mbeya in 1938 weighing about one kilo.

According to sources most Ivuna samples are held in private collections and by Tanzanian government. Its chemical make-up, which matches that of the sun, is extremely rare- just nine of the 35,000 known meteorites or 0.03 percent have this solar composition.

A meteorite curator at the Natural History Museum in London told the media that these types of meteorite are very susceptible to alteration on Earth. Changes in humidity for example could change their composition.

In 2009 the world will celebrate the International Year of Astronomy to commemorate the 400th anniversary of Galileo's first use of a telescope to study the night sky.

Astronomers around the world will be inviting people to look up in wonder at the night sky, and to seek out answers to some of life's biggest questions about our universe and its origins.

The theme of the years is ''The Universe -Yours to discover.''

Dr Caroline Smith unveils the Ivuna meteorite

A rare type of meteorite that could hold clues to the birth of our Solar System has been bought by London's Natural History Museum.

The Ivuna meteorite, obtained from a US private collection, has the same chemical make-up from which the Solar System formed 4.5 billion years ago. It landed in Tanzania in 1938 as one 705g stone, since split into samples.

Pieces from the UK sample, the largest in any public collection in the world, will be removed for study.

Most Ivuna samples are held in private collections, or by the Tanzanian government. It's a particularly important specimen to science because it's been so well preserved.

Dr Caroline Smith, meteorite curator at the Natural History Museum (NHM), told BBC News: ''These types of meteorite are very susceptible to alteration on Earth. Changes in humidity, for example, can change their composition.

''But this meteorite is important as it fell relatively recently and has been kept under nitrogen in a sealed environment for the last two or three decades.

''It's a particularly important specimen to science because it's been so well preserved. We're all incredibly excited about it because it's so pristine.''

Monica Grady, professor of planetary sciences at the Open University in Milton Keynes, commented: "This is fantastic for the UK's meteorite experts.

This material represents the crumbs from the foundation of the Solar System. It's an unbelievable opportunity to study it in close-up. The museum has been very bold in acquiring it.''

One question that Ivuna could help answer is how the chemical building blocks for life came to Earth. Important components of so-called pre-genetic material, the amino acids b-alanine and glycine, were found in Ivuna in a 2001 study.

Scientists at Imperial College London have confirmed that a meteorite called Murchison contained extra-terrestrial molecules that were the precursors to DNA and RNA.

In addition to being used for research, Ivuna will be a star specimen in a new meteorites gallery, which the NHM is planning for the near future.

''The plan is to take the meteorite to Nasa's Johnson Space Center in Houston, where we'll have a 20g piece taken off and that will be sub-divided into two 10g pieces,'' Dr Smith explained.

''One piece will be put to one side. The other will be divided into 200mg allocations - less than the size of your fingernail - for researchers to study."

Exploding Asteroid Theory Strengthened By New Evidence Located In Ohio, Indiana

Science Daily
Wed, 02 Jul 2008 18:47 EDT

©University of Cincinnati

Ken Tankersley

Ironically, Tankersley had gone into the field with West believing he might be able to disprove West's theory.

Much of the work is being done in Sheriden Cave in north-central Ohio's Wyandot County, a rich repository of material dating back to the Ice Age.

Tankersley first came into contact with West and Schaffer when they were invited guests for interdisciplinary colloquia presented by UC's Department of Geology this spring.

"The kind of evidence we are finding does suggest that climate change at the end of the last Ice Age was the result of a catastrophic event," Tankersley says.

Currently, Tankersley can be seen in a new documentary airing on the National Geographic channel. The film "Asteroids" is part of that network's "Naked Science" series.

The new discoveries made working with West and Schaffer will be incorporated into two more specials that Tankersley is currently involved with - one for the PBS series "Nova" and a second for the History Channel that will be filming Tankersley and his UC students in the field this summer. Another documentary, this one being produced by the Discovery Channel and the British public television network Channel 4, will also be following Tankersley and his students later this summer.

As more data continues to be compiled, Tankersley, West and Schaffer will be publishing about this newest twist in the search to explain the history of our planet and its climate.

Strange Asteroid Shapes Explained

Lee Pullen
Live Science
Thu, 03 Jul 2008 16:47 EDT

The asteroids that pepper our solar system come in all shapes, sizes and ages. What causes such a variety among space rocks has been something of a mystery, until now.

Researchers have been using a vast database to study a staggering 11,735 asteroids. They have discovered that asteroids change shape over time, and they think they know the reason why.

©Diagram: Minor Planet Center, Image: NASA/Johns Hopkins University Applied Physics Laboratory

The main belt is between the orbits of Mars and Jupiter, and contains countless asteroids.

Gyula Szabó from the University of Szeged [Hungary] is the lead author of the study, which was published in the July edition of Icarus. He explains, "There are several hundred thousand asteroids in our solar system. They orbit the sun, but because they are small their surface gravity is low. This means that many have strange, irregular shapes."

Scientists like Gyula think that about one third of known asteroids belong to groups called "families." These clusters probably formed from piles of debris after larger objects collided.

Resolved to save time

Determining the shapes of these asteroids presented difficulties for Gyula and his colleague Laszlo Kiss from the University of Sydney. The most accurate data about asteroids comes from spacecraft fly-bys, but only a few asteroids have been examined that way. Radar observations can only be made of objects that get close to the Earth. Telescopes produce detailed images, but only for the largest asteroids.

Another option for obtaining information about asteroids is called "time-resolved photometry." The technique is surprisingly simple: By observing asteroids as they spin in space and then studying the amount of light reflected, scientists can get an idea of their shape. Getting accurate results from this method can take a long time, but the researchers realised that digital sky surveys could speed up the process. Such projects study thousands of objects every night. The Sloan Digital Sky Survey, for instance, mainly looks at stars and galaxies, but it also has gathered data on asteroids.

"This procedure was very economical," says Gyula. "Using photometry, astronomers have determined shapes for about 1,200 asteroids in the past 30 to 40 years. We derived the shapes for ten times more asteroids, but in half an hour!"

Surprising results

"The results were really surprising," says Gyula. "We saw there were families that included many elongated asteroids, and there were other ones which consisted of mostly spheroidal bodies."

In young groups of asteroids there are a great variety of shapes, hinting that they formed relatively recently from fragments of rock that later bound together. Asteroids in older families tend to be rounder. It seems to take one billion to two billion years for irregular asteroids to be transformed into smooth balls.

But what changes the asteroids' shape? Gyula and his team have shown that asteroids change shape from elongated to roughly spherical due to being impacted during their lifetimes. They are like pebbles on the beach that become worn smooth over many years -- only in space, erosion is caused by small impacts as rocks knock into each other and chip pieces off.

Impact specialist Jonti Horner from the UK's Open University agrees with Gyula. "The results make sense," he says. "Catastrophic impacts create a huge slew of fragment shapes, like the shards of a broken bottle. The debris then are weathered over time and smoothed towards sphericality by small impacts."

Impacts are part of the fundamental processes in our solar system. They were part of the planet formation process 4.5 billion years ago, and still occur today. "Sometimes astronomers have to be archeologists, too," says Gyula. "This work is a fine example of how we can deduce a billion-year process from the world we observe today."

Hopefully, this research will not only teach us more about how the solar system operates, but will help us prepare for future impact events. Learning all we can about asteroids could help us avoid disaster if we ever detect a large, fast-moving one on a collision course with the Earth.

Rosetta awakes from hibernation for asteroid encounter

SpaceRef.com
Thu, 03 Jul 2008 12:30 EDT

Spacecraft controllers have just awoken Rosetta from hibernation to prepare for its encounter with asteroid (2867) Steins on 5 September. ESA's comet chaser will study the relatively rare asteroid as it flies by on its way to comet 67/P Churyumov-Gerasimenko.

Launched in March 2004, Rosetta will reach its final destination only in 2014, after travelling a total of about 6500 million km. The distance between the spacecraft and the Sun as it approaches the comet will be about 600 million or 4 AU (1 AU or 1 Astronomical Unit is equal to 150 million km, the mean distance between Earth and the Sun).

Rosetta has swung by Earth twice and Mars once, performing gravity-assist manoeuvres, that gave it the necessary boost to continue on its journey. The third and last Earth swing-by is scheduled for November 2009. The spacecraft will also fly by two asteroids and study them on the way: (2867) Steins in September this year and (21) Lutetia in June 2010. As it closes in on (2867) Steins in September, Rosetta will have travelled about 3700 million km and will be 2.1 AU from the Sun.

After its last planetary swing-by on 13 November last year, Rosetta headed towards the asteroid belt located between the orbits of Mars and Jupiter. On 27 March 2008, the spacecraft switched to its near-Sun hibernation mode for a period of three months. During this phase, a few subsystems were put into a dormant state to optimise their lifetime (as this is only the beginning of the mission's science phase).

Rosetta will be closest to (2867) Steins at 20:37 CEST on 5 September, at a distance of 800 km. The spacecraft will zoom past at a relative speed of 8.6 km/s.

In preparation for the fly-by, all the instruments will be checked and tested through the month of July. Between 4 August and 4 September, spacecraft operators will conduct an optical navigation campaign: Steins will be tracked by the on-board cameras and the observations will be used to refine the knowledge of its orbit which has been derived only from ground-based measurements so far.

Asteroids are samples of the Solar System's material at different stages of evolution, and studying them helps scientists understand the origin and evolution of Earth and of our planetary neighbourhood.

(2867) Steins is a relatively rare type of asteroid. Based on ground-based observations it has been classified as an E-type asteroid, composed mainly of silicates and basalts, but its properties are not known in detail. For these reasons, it has been selected as one of the two asteroids that Rosetta will study, from among those that were within reach of the mission. The knowledge gained from the measurements will add to our knowledge of the composition and evolution of E-type asteroids and will also supplement and help interpret future ground-based data on asteroids.

The observations will be used to characterise the asteroid and its environment and to test Rosetta's instruments, most of which will be active during the fly-by.

The science objectives of the fly-by observations are as follows:

To characterise the asteroid by studying its physical and chemical properties
To study its kinematic properties (its rotation, for example)
To study the asteroid's surface and to perform comparative studies with surfaces of other asteroids in order to understand differences between asteroid types
To study the interaction between the solar wind and the asteroid
To study the asteroid's environment, including the presence of natural satellites, the magnetic and electrical properties of the immediate environment, and gas or dust orbiting the asteroid

The fly-by will push Rosetta to its design limits, especially owing to the fast rotation of the spacecraft around the time of closest approach. The manoeuvre is necessary to ensure that the asteroid will stay in the field of view of the instruments. In view of this, a full in-flight simulation of the fly-by was performed on 24 March 2008. The tests were successful, confirming the spacecraft's robustness.

Major journey milestones

Launch 2 March 2004
First Earth swing-by 4 March 2005
Mars swing-by 25 February 2007
Second Earth swing-by 13 November 2007
Third Earth swing-by 13 November 2009
Comet 67/P Churyumov-Gerasimenko rendez-vous May 2014
Landing on the comet November 2014
Escorting the comet until end 2015

Was rocket moments from striking Continental flight?

Houston Chronicle
Thu, 03 Jul 2008 08:36 EDT

Probe of launch near Bush airport has stalled, FAA records indicate

A Continental airliner might have been only a minute away from colliding with what the pilot described as a model rocket that shot past his cockpit window, Federal Aviation Administration records obtained by the Houston Chronicle show.

On Memorial Day, the Continental pilot reported being startled by his encounter with this object that "went straight up" and left a long white vapor trail.

Yet the trail to identifying this object has appeared to run cold since the FAA and the FBI's Joint Terrorism Task Force launched their investigation into the episode.

For starters, the radar at George Bush Intercontinental Airport was unable to detect any unusual object in the sky when Flight 1544 took off. A video recording, acquired from the FAA through a Chronicle open record request, shows the radar detected nothing but dozens of airplanes.

FAA authorities said this is not surprising because airport surveillance radar is designed to track the departure and arrival of planes, and officials want to avoid clutter. It would usually not pick up a small object such as a model rocket that is going straight up, the FAA said.

The radar data also show the plane carrying 148 passengers to Cleveland never detoured from its route.

Just minutes after takeoff, as the plane was headed over Lake Houston, the pilot acknowledged spotting the object. The plane had then reached 4,750 feet elevation and was traveling at 277 mph, records show.

'Is that a rocket launch?'

The pilot on that flight, Capt. George Drebo, has declined to comment. The co-pilot, John Knight, could not be reached.

But radio conversation between the plane and air traffic control showed the pilot's surprise at encountering something in his airspace.

"Can you tell me what this is on my 12 o'clock (in front of his plane)? It's climbing about 20 miles up. Is that a rocket launch?" he asks.

The control tower responds: "I am unaware of any activity in your vicinity."

Later, the pilot adds, "Oh, it's going straight up!"

As a precautionary measure, for about an hour, the FAA placed a temporary flight restriction over the area where the object was seen.

Some residents reported seeing F-16 fighter jets across the area, but the Air National Guard did not return phone calls about the jets.

The air traffic controller also was recorded asking other pilots flying in the area what they saw.

"On your climb out, did you happen to see any rocket launches in your vicinity?" the tower dispatcher asks.

"Negative," said a pilot on Flight 2168.

"OK. Just checking on something."

Flight 1544's pilot soon chimes in to say again: "It went straight up!"

Later, the dispatcher asks another pilot if he saw a "rocket launch" about "three to four miles out."

"Don't mean to alarm you, but there might be a possibility that you will see it," the dispatcher said.

That pilot answers, "See some contrail up here, but that's about it."

At another point, the air traffic dispatcher asks another pilot to radio crew members of Continental 1544 and ask them for a better description, such as the object's size and if it resembled a model rocket.

"We're trying to figure out a location to see if this is a problem for us," the dispatcher said.

He tells another pilot who spotted the contrail that "we're keeping you south of that suspected area."

At the speed the plane was flying, the aircraft was only about a minute away from a collision if the plane and object were four miles apart, authorities said.

The dispatcher has indicated the object was about three or four miles from the plane, while an FBI spokesman Rich Kolkohas estimated "a mile or two."

Public's help welcome

FBI spokeswoman Shauna Dunlap, who said her agency routinely looks into suspicious activity involving aircraft, said agents have not yet identified what the pilot saw.

She could not discuss the specifics of the investigation, but said the agency would welcome anyone who might have information about the incident.

No hobby clubs had requested or been granted clearance to launch any high-powered model rockets on the May 26 holiday.

Rocketeers, as the hobbyists call themselves, must obtain special waivers from the FAA to fly rockets in controlled airspace.

In addition, they are fingerprinted and undergo background checks by the Bureau of Alcohol, Tobacco, Firearms and Explosives before they can buy the high-powered engines that propel such rockets.

FAA rules also would have prohibited this launch because it was located too close to an airport, authorities said.

When asked whether a model rocket could seriously damage an airliner, FAA spokesman Roland Herwig has declined to speculate. "There are so many variables. It depends on the circumstances. How fast is it going? How big is it? Is it coming at them or are they chasing it?"

Marlene McClinton, spokeswoman for Houston Airport System, said, "We have no idea if such a model rocket could be dangerous. But common sense tells you that anything hitting a plane is not good."

Model rockets are equipped with parachutes and other devices to bring them safely to the ground for reuse.

They can be made of anything from cardboard to aluminum.

Jenni Etgen, treasurer of the Houston Chapter of Tripoli Rocketry Association, said some models that soar the highest can weigh 150 pounds, stand 11 feet tall and be 6 inches in diameter.

She wondered whether the object might have been some sort of fireworks.

Canada: Fireball in sky not a plane, Halifax police say

CBC
Thu, 03 Jul 2008 18:48 EDT

Police investigating a report of a small plane crashing in Halifax say the glowing object was likely a flare.

Comment: Or a meteorite.

A group of children reported that a fireball nosedived to the ground in a wooded area off Herring Cove Road Wednesday evening.

Firefighters, police and search-and-rescue teams sprang into action. As a helicopter searched from above, police rode dirt bikes through the woods.

But as the investigation continued, it was appearing less likely that the object was a plane.

Police said they were told that someone had fired a flare nearby, which matched the trajectory of the object the children saw.

The helicopter didn't find wreckage, no airports had light planes in the air at the time, and no one else reported seeing a plane go down, police said.

The search was called off shortly after dark.

Peru Meteorite could have survived descent if it lacked internal cracks and irregularities

ANI
Fri, 04 Jul 2008 18:41 EDT

Scientists have said that a meteorite that crashed in Peru in September last year may have survived the descent towards Earth if, by a one-in-a-million chance, it lacked internal cracks and irregularities.

According to a report in New Scientist, the Carancas meteorite struck the town of that name in Peru last September, blowing a hole in the ground 13 metres wide.

The fact that locals saw a single object strike suggests a meteorite made of iron, like the one that created a similar crater in 1990 in Sterlitamak, Russia, because stony meteorites normally fragment high above the Earth and spread relatively harmlessly over a wide area.

However, the debris found by investigators was stone.

"Stony meteorites normally fragment high up above the Earth and spread harmlessly over a wide area," said the researchers.

One explanation for this conundrum, though at odds with the eyewitness accounts, is that the object broke into smaller pieces, which hit the ground together.

Another theory is that the meteorite was one of many chunks from a larger, slow-moving object which broke up when it met the atmosphere at a glancing angle. Yet all these chunks would probably have been traveling too slowly to create the Carancas crater.

Now, Pavel Spurny and colleagues at the Astronomical Institute of the Academy of Sciences of the Czech Republic argue that the object could have survived the descent intact if, by a one-in-a-million chance, it lacked internal cracks and irregularities.

Using estimates from other groups of the meteorite's trajectory, velocity and impact energy, Spurny and colleagues built a computer model showing that an object around 1 metre across could enter the atmosphere at a relatively fast 20 kilometres per second and survive the descent if it was free of cracks.

Asteroid And Comet Threat Is A Challenge To Mankind

Reuters
Sat, 05 Jul 2008 11:25 EDT

ST. PETERSBURG -- The asteroid and comet threat is a real challenge to mankind in the 21st century, and it is described as "space terrorism", Russia's Itar-Tass news agency reported Saturday quoting the Director of the Institute of Applied Astronomy Andrei Fenkelshtein, as saying.

Speaking at the regional Itar-Tass centre, Fenkelshtein said: "This phenomenon is well studied from the scientific point of view even though speculations continue to revolve around the event that occurred one hundred years ago."

In his opinion, what happened in Southern Siberia is "a serious warning to the earthlings.

Filkenshtein, who is also the correspondent member of the Russian Academy of Sciences, said the risk of a new event like the Tunguska explosion is assessed as quite plausible now that scientists have detected potential killer Asteroid Apophis just half a million kilometers from Earth, which is an infinitesimally small distance by astronomical standards.

Most experts agree that Apophis requires closer scrutiny, and to that end, in February 2008 the Planetary Society awarded US$50,000 in prize money to companies and students who submitted designs for space probes that would put a tracking device on or near the asteroid.

According to mathematical modeling data, if an asteroid several kilometres wide or a comet nucleus collides with the planet, "mankind may be wiped out of the face of Earth instantly or may be thrown back several centuries in its development".

If a space body falls into the oceans, the effect will be "much more devastating than, for example, seismic tsunami", Filkenshtein said.

He said: "The impact of a rock asteroid some 500 metres in diameter on the surface of the ocean at a speed of 10-20 meters per second will create a cavern causing circular waves that may come as high as four kilometers in the centre and 300-400 metres when they hit the continents."

He believes it is quite likely that similar events "caused 90 percent of all animals on Earth to die millions of years ago".

Maybe Chicken Little Wasn't Paranoid After All

Anrew C. Revkin
New York Times
Sat, 05 Jul 2008 23:58 EDT

The Earth is pockmarked with the evidence of ancient collisions - huge craters blasted into its surface by asteroids or comets. One such object, striking 65 million years ago in the Yucatán in Mexico, is believed by some experts to be linked to the demise of the dinosaurs.

For a decade, NASA has been busy trying to identify what else is headed this way, particularly those potential "civilization killers" of 1 kilometer (.62 miles) or more in diameter that have orbits coming within 30 million miles of the Earth's - too close for comfort by space standards.

But the big ones are, in many ways, the easy part. Smaller rocks matter, too. Perhaps nowhere is that so evident as in central Siberia, where 100 years ago last week, something - presumably a meteoroid, most experts say - streaked across the sky and exploded at an estimated height of 28,000 feet with a force equivalent to 185 Hiroshima bombs, leveling some 800 square miles of forest. Simulations by the Sandia National Laboratories showed that object could have been just 90 feet across.

The explosion that lit up the Siberian sky in a fireball shortly after 7 a.m. on June 30, 1908, is known as the Tunguska event, after the river the flows through the damage zone, and is widely considered the modern-day warning about the dangers slinging through space.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., has estimated that a Tunguska-size asteroid will enter Earth's atmosphere once every 300 years and says there may be 375,000 objects of such size out there.

Fortunately, the odds are good that the next one will fall over one of our oceans, which take up more than two-thirds of the Earth's surface, or the planet's still-vast stretches of uninhabited lands. How much in taxpayer dollars should be invested to pinpoint such hazards is one of the toughest risk-management exercises around.

Donald K. Yeomans, who manages the jet propulsion lab's Near-Earth Object Program, said the Earth's atmosphere is continually streaked by space stuff, ranging from the basketball-size (several a day) to the Volkswagen-size (twice a year). Almost everything burns up, though some may explode in the air, a phenomenon known as an airburst, with the potential of causing damage below. And then there are objects, like the meteorite that dug a 60-foot-wide crater in Peru last September. Perhaps no bigger than a basketball, the meteorite was a reminder of the destructive power of what is lurking out there.

"In fact, there was a daylight fireball event widely observed near Los Angeles two days ago," Dr. Yeomans said in an e-mail message last Thursday. "I take these events as Mother Nature's little reminders that we need to pay attention, find and track the large ones and then deflect the very few that threaten us. Tunguska was another reminder. Until recently, we humans did not pay heed to these shots across the bow but now, I think, there is more of a recognition of this low probability - but high consequence - type of event."

NASA estimates that there are about 940 or so near-Earth space rocks a kilometer in diameter or larger. So far, according to Dr. Yeomans, NASA has identified 743. (Overall, NASA has pinpointed more than 5,500 near-Earth objects.)

Budget constraints have slowed NASA's efforts to meet its goal of identifying 90 percent of those big objects by next year. As for rocks similar in size to the one that exploded over Siberia, a NASA search is probably a long way down the line.

Even so, one way or the other, many more potential incoming asteroids will be identified in the next decade, astronomers say. But awareness is just the first stage of grappling with the challenge, said Rusty Schweickart, the Apollo 9 astronaut who heads a foundation advocating more research on identifying near-Earth objects and developing unmanned spacecraft that could nudge them off track like a tugboat.

Mr. Schweickart said progress so far had come through constant pushing against resistant bureaucracies and politicians focused on whatever is the issue of the moment. And he said there was still no significant effort to devise an international agreement, let alone a deflection technique, for dealing with the inevitable earthbound asteroid or comet, large or small, when it is identified.

"It may be subtle," he said, "but failure of the international decision process is the most likely reason that we'll take a hit in the future.

U.S. urged to prepare for asteroid strike

Yan Liang
China View (Xinhua)
Sun, 06 Jul 2008 18:21 EDT

U.S. scientists have urged the U.S. government to take further defensive measures against near-Earth objects, The Los Angeles Times reported on Saturday.

The United States was not doing enough to defend the planet against the dangers posed by near-Earth objects, said a group of scientists who observed the 100th anniversary of the Tunguska asteroid event this week in Los Angeles.

"We are not prepared at this time to prevent the massive death and destruction that would occur if an object from space hit the Earth as it did in Tunguska" in Siberia, said Republican Congressman Dana Rohrabacher who joined the scientists in the event.

He was referring to an explosion in the air above Tunguska, a remote river valley in eastern Russia on June 30, 1908, which flattened trees over an 800-square-mile (1280-square-kilometer) area, but no one was killed. Although no one is positive what caused the Tunguska event, most scientists believe an asteroid about 150 feet across exploded.

If an asteroid the size of the one believed to have exploded in the air above Tunguska were to explode over Los Angeles, the destruction would be greater, Rohrabacher told a news conference at the Pasadena offices of the Planetary Society in Los Angeles.

NASA has established a Near-Earth Object Program Office at the Jet Propulsion Laboratory in Southern California to monitor potentially dangerous asteroids. The most scrutinized is Apophis, which has about a one-in-45,000 chance of hitting Earth in 2036, according to Don Yeomans, manager of the Near-Earth Object Program Office. Apophis is about five times the suspected size of the Tunguska object.

But Alan Harris, a senior research scientist at the Space Science Institute in Boulder, Colorado, said the greatest danger does not come from the objects we know about but from the ones we haven't identified.

In one example of the lack of attention the issue is receiving in Washington, Rohrabacher said, funding for the Arecibo, Puerto Rico, radio telescope, which hunts near-Earth objects, is in danger in next year's budget.

If scientists are able to identify a potential killer asteroid, the deeper question is how to deflect it.

Theorists have proposed a variety of possible solutions, including using a nuclear weapon to blow it up or sending a spacecraft that would use gravity to drag the object off its destructive path.

Comment: A big problem is the misrepresentation of the situation; of suppression and inconsistency within scientific knowledge on the subject, as highlighted by SoTT's "Comets and Catastrophe's" series.

A common misconception is that any threat comprises a single massive impact, whereas research from the likes of Victor Clube (whose work is wholly suppressed) indicate that a more realistic threat comes from dispersed but dense clusters of numerous cometary fragments and dust, within the Taurid stream, rather than a single massive 'lump'. This could make the 'deflect the asteroid' solution wholly ineffective.

See 'The Cosmic Winter' by Victor Clube and Bill Napier for more information.

Witness account: Large meteorite seen over Cyprus

SOTT
Tue, 08 Jul 2008 17:17 EDT

Between 8:25 - 8:30 pm tonight, in the town of Larnaca (Southern coast of Cyprus) I was walking by the beach when I saw in the sky something like a ball of fire moving slower than a usual falling star, followed by a bright pink/red tail. Other people on the beach saw it as well and kept talking and wondering about it.

None of us saw anything like this before. It must have been much closer to the earth than "regular" falling stars, because we kept seeing it crossing the sky for about 10 seconds before it disappeared from view behind some tall buildings.

It seems to have been going north, somewhere over Turkey, or maybe even Greece.

Comment: It appears that this is the same meteorite that was seen crossing Israeli sky at 08:15 pm.

Large meteor crosses Israeli skies

Jerusalem Post
Tue, 08 Jul 2008 16:52 EDT

A large meteor crossed Israel's skies on Tuesday evening, and was seen by many residents, mainly in Samaria, Army Radio reported.

According to citizens' reports, the object was seen at approximately 8:15 p.m., as it crossed the sky from east to west horizontally. Some witnesses said they saw two shiny objects in the sky, and others reported that they heard a shrieking sound.

A Petah Tikva resident told Army Radio that he saw a beam of light, which crossed the sky in the direction of the sea. "It looked like a comet, with a long white tail, but much shinier and moving much faster," he said.

Yigal Pat-El, chairman of the Israeli Union of Astronomers, told Army Radio that the meteor was exceptionally large, and that its entry into the atmosphere was not expected.

Nevertheless, he emphasized that this was not an uncommon occurrence.

"Meteors enter the Earth's atmosphere all the time - it's not a rare phenomenon. The meteor was relatively large - most do not weigh a thousandth of a gram, and it seems this meteor would have weighed a few grams," he said.

Ball Of Fire Spotted On Heathrow And Gatwick Flightpath

Jon Vickery
Compare Airport Parking News
Tue, 08 Jul 2008 16:34 EDT

Saturday night saw another UFO report come in that involved a UK airport. The recent sightings near Cardiff Airport by a police helicopter caused a wave of excitement, especially due to the creditability of the witnesses - a pilot and police officers. However it came to light that the sightings were more than likely down to paper lanterns released at a local wedding.

The new sighting near Gatwick Airport however is a very different story. The Parker family from Mutton Hall Hill have reported seeing a ball of flames streaking across the sky, that appeared to be taking the same path as aircraft heading for Gatwick and Heathrow Airport from the continent in a northwards direction.

However, apparently the UFO then veered off to the east and vanished. The Parker family accept that it may have been a military flare as it did appear to travel with the wind although a flare from a distance often does not look like a ball of flames and more like a light. However as ususal any developments on the story will be covered here on Compare Airport Parking.

Officials: Blasts heard near Pakistani capital may have been from sonic boom

Associated Press
Mon, 30 Jun 2008 14:03 EDT

Investigators found no physical evidence of loud explosions heard Monday near the Pakistani capital and officials said it may have been a sonic boom caused by fast-moving aircraft.

The blasts were heard in Rawalpindi and the capital, Islamabad, two cities about 7 miles (12 kilometers) apart. Rawalpindi houses the headquarters of
Pakistan's army and the residence of President Pervez Musharraf, a key U.S. ally in the war on terror.

'All sensitive installations are clear,' said Rao Mohammed Iqbal of the Rawalpindi police.

Hours after the explosive sounds echoed through the area, there were no reports of any detonation site having been found.

Air Cmdr. Humayun Waqar Zephyr, a Pakistan air force spokesman, said authorities were looking into whether an aircraft caused a sonic boom after taking off from an air base outside Islamabad.

But 'there was no flying activity' in the immediate vicinity of the two cities, he said.

He said that in clear weather conditions the boom of a jet crossing the sound barrier can reach Islamabad from nearby air bases. He declined to specify any distance for any base near the capital.

Lack of cracks may explain Peru meteorite mystery

Devin Powell
ScientistSpace
Thu, 03 Jul 2008 14:33 EDT

It's the Superman of space rocks. A mysterious meteorite that crashed to Earth last year may have been the toughest of its kind.

The Carancas meteorite struck the town of that name in Peru last September, blowing a hole in the ground 13 metres wide. The fact that locals saw a single object strike suggests a meteorite made of iron, like the one that created a similar crater in 1990 in Sterlitamak, Russia, because stony meteorites normally fragment high above the Earth and spread relatively harmlessly over a wide area. However, the debris found by investigators was stone.

One explanation for this conundrum, though at odds with the eyewitness accounts, is that the object broke into smaller pieces which hit the ground together. Another theory is that the meteorite was one of many chunks from a larger, slow-moving object which broke up when it met the atmosphere at a glancing angle. Yet all these chunks would probably have been travelling too slowly to create the Carancas crater.

Now Pavel Spurný and colleagues at the Astronomical Institute of the Academy of Sciences of the Czech Republic argue that the object could have survived the descent intact if, by a one-in-a-million chance, it lacked internal cracks and irregularities. Using estimates from other groups of the meteorite's trajectory, velocity and impact energy, Spurný and colleagues built a computer model showing that an object around 1 metre across could enter the atmosphere at a relatively fast 20 kilometres per second and survive the descent if it was free of cracks (Astronomy & Astrophysics, vol 485, p L1).

Jay Melosh, a geophysicist at the University of Arizona in Tucson, doubts Spurný's theory. He says stone fragments found at the scene are so soft that they crumble to the touch, so the object was probably made of rock held together by iron - which is yet to be found.

Comets and Asteroids - Learn more about the threat to human civilisation in our special report.

South Africa: 'UFO' mystery along Cape coast

News24.com
Sun, 06 Jul 2008 08:34 EDT

Cape Town - Was it an Unidentified Flying Object, was it a ship in distress or was it just people firing off red distress flares? The mystery remains...

Mark Thompson, NSRI Bakoven station commander says it all started at about 21:10 on Saturday when their station was alerted to a red distress flare sighting about 500m off-shore at Bantry Bay.

"Within minutes of this report, further ones of distress-flare sightings were received from Lambert's Bay, Yzerfontein, Bakoven, Hout Bay, Strandfontein on the West Coast, and also from Gansbaai (on the south coast).

Thompson said: "All sightings reported were from credible and co-operative witnesses."

One vessel known to be at sea at this time was the 37ft yacht, Mr B, sailing from Cape Town to Langebaan.

No meteor acitvity

It had left Cape Town at 13:00 on Saturday and could not be contacted, the location and fate of the yacht remaining a mystery.

Dr Peter Martinez of the SA Astronomical Observatory confirmed that while there were no significant reports of meteor activity at the time of the reports, the possibility could not be completely ruled out.

Further investigations would be conducted to assist in determining the possibility of meteor activity and/or space craft re-entry.

Thompson said NSRI Table Bay launched the rescue craft Spirit of Vodacom and a search operation covering Table Bay and along the Atlantic Seaboard was initiated.

"As the search operation progressed, NSRI Hout Bay launched rescue craft MTU Nadine Gordimer to join in the search.

"NSRI stations at Bakoven, Yzerfontein, Lambert's Bay and Mykonos were all alerted and volunteers posted along the coast to watch for further flare sightings.

Shot from car park

"They also were to investigate for any overdue vessels and to investigate boat trailers abandoned at launching sites that might suggest vessels or craft still at sea.

"NSRI Hermanus investigated a flare report near Gansbaai which appeared to be unrelated to the suspected flares reported along the West Coast after police confirmed witnesses seeing the flare being activated near a car park in town."

"After the search, covering a vast area of the West Coast, the 'missing' Mr B yacht was confirmed to be safe at Langebaan about 09:00 on Sunday morning.

"Along the West Coast, witnesses were questioned extensively on what they saw.

No signs by 03:00

"It appeared to be similar type of sightings with most witnesses claiming what they thought was a flare arcing downwards at a 70-degree angle, very bright and appearing to be very close in-shore and very close to the person observing the sight.

"NSRI rescue craft covered a large area searching for any signs of vessels in distress, but by 03:00 no signs of vessels in distress or further reports of flare sightings led to rescue craft being recalled until new information could verify a rescue requirement.

"Maritime Radio Services broadcast an all-ships alert and there were no further suspected flare sightings."

Meteor sparks fears of UFO, Iranian missiles in Israel

Israel Today
Wed, 09 Jul 2008 23:47 EDT

A relatively large and unexpected meteor streaked across the sky over central Israel Tuesday evening, sparking widespread fears that the nation was under attack by Iran, Syria, or perhaps aliens.

The large bright ball and flaming tail were visible around 8 PM and were seen by thousands of Israelis from Jerusalem to Tel Aviv. As soon as the meteor had disappeared, burned up in earth's atmosphere, calls to the police began pouring in.

Panic-striken Israelis were certain that one of Israel's many regional enemies was finally making good on threats to destroy the Jewish state. Just as many callers believed the celestial sighting was a UFO.

Officials said the atmosphere of near hysteria was only made worse by the fact that astronomers had failed to predict this particular meteor would hit earth. One astronomer said he and his colleagues rarely miss predicting such a large meteor colliding with earth's atmosphere.

Solar-powered asteroids make their own moons

Devin Powell
New Scientist
Wed, 09 Jul 2008 17:39 EDT

Most asteroids with moonlets started off as solitary bodies that split in two while sunbathing, new computer simulations suggest.

Once thought to be rare, dozens of binary asteroid systems - kilometre-sized rocks orbited by small moonlets - have been found in the main belt between Mars and Jupiter since the first asteroid pair was spotted by the Galileo spacecraft in 1993. And 15% of all near-Earth asteroids, which cross Earth's orbit, boast satellites.

Various theories have been proposed to explain how they formed. One suggests the pairs were created by collisions between older asteroids, but because of the huge distances between objects in space, such impacts are very rare.

©Kevin Walsh/Derek Charles Richardson/UMD

Pairs of asteroids can be created from a single parent body that spins so fast due to solar energy that it breaks apart. In new computer simulations, the parent body was modelled as a rubble pile. Loose material near its poles rolled to its equator, then floated off to become a moon

Collisions may account for some large pairs of asteroids in the main belt, where asteroids orbit for billions of years, but the smaller near-Earth asteroids are much more likely to crash into the Sun or one of the inner planets before colliding with each other.

Another concept - tidal disruption - suggests that the strong gravitational pull of a planet can tear a passing asteroid in two to create a couple. The problem with this explanation is that the planet is even better at separating the members of this newborn couple when they cross its path again on another orbit.

Now, computer models bolster the case for a third explanation. Kevin Walsh of the University of Maryland in College Park, US, and colleagues say solar energy can cause single asteroids to rotate fast enough to break apart and create their own moons.

As an asteroid soaks up sunlight, it gives off energy in the form of heat - like a sidewalk in the summertime. Because its surface is uneven, the tiny jet streams of hot photons give the rock an overall rotational force, called the YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) effect.

Rubble piles

To test whether the YORP effect could have formed a near-Earth object called 1999 KW4 and its moon, Walsh and colleagues developed computer models of spinning asteroids.

Like many asteroids, 1999 KW4 and its moon appear to be "rubble piles" - loose rocks and boulders held together by gravity. The larger asteroid is shaped like a flying saucer 1.5 kilometres in diameter and is orbited every 16 hours by its small round companion.

©Steve Ostro/NASA/JPL

In 2006, the Arecibo Observatory bounced radio waves off of the flying-saucer-shaped asteroid 1999 KW4 (top) and its moon (bottom), creating the best 'pictures' of an asteroid pair ever made

In the simulations, the team spun rubble piles of various shapes, sizes and consistencies. As each object heated up and began to spin faster, loose material at its poles tended to roll to its equator. This caused the asteroid to "bulge outwards in the middle like a hamburger", team member Derek Richardson of the University of Maryland told New Scientist.

Critical speed

At a critical speed and shape, small bits near the edge of the disc gently floated off into orbit around the asteroid. Over time, gravitational attraction drew the pieces together into a growing clump, which was fed by the steady stream of ejected matter. And a binary system was born.

The process, which should take hundreds of thousands of years out in space, is displayed in 27 seconds on a computer screen (the right panel shows an equatorial view of the pair, while the left panel shows the pair from above).

The results "delightfully resemble the real-world case" of 1999 KW4 and other near-Earth pairs, says Stephen Lowry of NASA's Jet Propulsion Lab in Pasadena, California, US.

Lowry, who published the first detection of the YORP effect in 2007, also notes that these simulations support the increasingly popular idea that kilometre-sized asteroids are conglomerations of boulders, not solid pieces of rock.

Discovery of the source of the most common meteorites

Astronomy & Astrophysics
Fri, 11 Jul 2008 16:39 EDT

When observing with the GEMINI telescopes, two astronomers from Brazil and the United States discovered for the first time asteroids that are similar to "ordinary chondrites", the most common meteorites found on Earth. Until now, astronomers have failed to identify their asteroidal sources because of the various geologic processes that occur after the meteorites are ejected from their asteroidal parent body. This discovery is being published this week in Astronomy & Astrophysics.

Astronomy & Astrophysics is publishing the first discovery by T. Mothé-Diniz (Brazil) and D. Nesvorný (USA) of asteroids with a spectrum similar to that of ordinary chondrites, the meteoritic material that most resembles the composition of our Sun. Most of the meteorites that we collect on Earth come from the main belt of asteroids located between Mars and Jupiter [1]. They were ejected from their asteroidal "parent body" after a collision, were injected into a new orbit, and they finally felt onto the Earth. Meteorites are a major tool for knowing the history of the solar system because their composition is a record of past geologic processes that occurred while they were still incorporated in the parent asteroid. One fundamental difficulty is that we do not know exactly where the majority of meteorite specimens come from within the asteroidal main belt. For many years, astronomers failed to discover the parent body of the most common meteorites, the ordinary chondrites that represent 75% of all the collected meteorites.

To find the source asteroid of a meteorite, astronomers must compare the spectra of the meteorite specimen to those of asteroids. This is a difficult task because meteorites and their parent bodies underwent different processes after the meteorite was ejected. In particular, asteroidal surfaces are known to be altered by a process called "space weathering", which is probably caused by micrometeorite and solar wind action that progressively transforms the spectra of asteroidal surfaces. Hence, the spectral properties of asteroids become different from those of their associated meteorites, making the identification of asteroidal parent body more difficult.

Collisions are the main process to affect asteroids. As a consequence of a strong impact, an asteroid can be broken up, its fragments following the same orbit as the primary asteroid. These fragments constitute what astronomers call "asteroid families". Until recently, most of the known asteroid families have been very old (they were formed 100 million to billions of years ago). Indeed, younger families are more difficult to detect because asteroids are closer to each other [2]. In 2006, four new, extremely young asteroid families were identified, with an age ranging from 50000 to 600000 years. These fragments should be less affected than older families by space weathering after the initial breakup. Mothé-Diniz and Nesvorný then observed these asteroids, using the GEMINI telescopes (one located in Hawaii, the other in Chile), and obtained visible spectra. They compared the asteroids spectra to the one of an ordinary chondrite (the Fayetteville meteorite [3]) and found good agreement, as illustrated on Fig. 1.

©Arkansas Center for Space and Planetary Sciences, University of Arkansas

Fig. 1 - (Right) Comparison of the spectrum of asteroid (1270) Datura with the spectrum of the Fayetteville meteorite. (Left) Pictures of the Fayetteville meteorite

This discovery is the first observational match between the most common meteorites and asteroids in the main belt. It also confirms the role of space weathering in altering asteroid surfaces. Identifying the asteroidal parent body of a meteorite is a unique tool when studying the history of our solar system because one can infer both the time of geological events (from the meteorite that can be analyzed through datation techniques) and their location in the solar system (from the location of the parent asteroid).

***

[1] There are only a few exceptions, including the example of the famous meteorites coming from Mars.

[2] After the primary asteroid is disrupted, the fragments move away from each other. The older the collision, the greater the distance between fragments.

[3] Meteorites are named for the place they were collected. The Fayetteville meteorite fell near Fayetteville, Arkansas, on December 26, 1934.

***

Visible spectroscopy of extremely young asteroid families, by T. Mothé-Diniz and D. Nesvorný

Astronomy & Astrophysics Letters, 2008, volume 486-2, pp. L9-L12. Full article available in PDF format

Sunlight Splits Asteroids into Pairs

Clara Moskowitz
Live Science
Sat, 12 Jul 2008 20:00 EDT

Asteroids often come in pairs, with the two objects spinning around each other. Now scientists say sunlight could be the cause of these binary boulders.

A new study suggests energy from the sun can spin up a single asteroid until it ejects material that becomes a separate satellite.

©diagram - Minor Planet Center; image - NASA/Johns Hopkins University Applied Physics Laboratory

The main belt is between the orbits of Mars and Jupiter, and contains countless asteroids.

Astronomers first discovered these strange asteroid pairs 15 years ago, and have been puzzled about what causes them. Now scientists have created a computer model that matches what they see.

"So far our results match the properties of binary asteroids quite well," said astronomer Kevin Walsh of the Observatoire de la Cote D'Azur in Nice, France. Walsh led the study when he was a graduate student at the University of Maryland, working with his advisor Derek Richardson and Patrick Michel of the Cassiope'e, University of Nice-Sophia Antipolis, in Nice.

Lots of them

Binary asteroid systems are surprisingly common - they seem to make up about 15 percent of near-Earth asteroids, or those that come near our planet's orbital path around the sun. (Most asteroids orbit in a belt between Mars and Jupiter and are too far from Earth for detailed measurements).

In order to probe how these binary setups are spawned, the astronomers modeled asteroids as "rubble piles," or chunks of rock held together by gravity, and watched what happened over time. The thinking is that many asteroids are not solid objects but rather loose conglomerations prone to rearrangement and pulling apart.

When sunlight hits one of these piles, the material absorbs some of the radiation and then re-emits it at a slightly different angle, giving itself a small push in angular momentum, Walsh said. This change can cause the asteroid to spin up slightly in what's called the YORP effect (named for the scientists who discovered it: Yarkovsky-O'Keefe-Radzievskii-Paddack).

The YORP effect is also known to slow down the spin of some asteroids and tweak the orbits of others, sending them flying in slightly different directions, and occasionally toward another planet, such as Earth.

Over time, as an asteroid spins up, its shape will become more spherical with an increasingly circular equator where mass begins to build up. Eventually, if the rock spins fast enough, the force outward from the rotation will overpower the gravitational pull inward and material will eject along the equator to form a new small satellite. The two asteroids then circle each other in binary pairs.

"Ours was the first model that could actually simulate an asteroid being spun up to its maximum spin rate by the YORP effects," Walsh told SPACE.com. "We made the first step and showed YORP can make systems that look exactly like what we observe."

Not the only way

The team compared their model's predictions to observations of a binary asteroid called KW4 made by astronomers using the Arecibo radio telescope in Puerto Rico.

"It's by far the best observation we have of any single asteroid," Walsh said. "Globally, observations suggest that nearly all the small near-Earth binary systems are similar to this KW4 system. We recreate its shape pretty closely with a lot of our simulations."

Though the scientists say the YORP effect isn't the only way to create binary systems - they could also be formed by impacts or by tidal forces from passing another large body - they think the process they've modeled accounts for most of the known asteroid pairs.

Icy asteroids: Resident asteroids sprout comet-like dust tails

Ron Cowen
Science News
Thu, 17 Jul 2008 23:53 EDT

Oh, for the good old days, when asteroids were asteroids and comets were comets! In the simplest model of the solar system, which most planetary scientists had accepted for decades, asteroids are rocky, geologically dead bodies and comets are icy objects that flaunt majestic dust tails when they near the sun.

©Hsieh, Jewitt

Although all three of these objects lie in the asteroid belt, they flaunt comet-like dust tails and are known as main-belt comets. New observations and models are further blurring the line between comets and asteroids.

That definitional dividing line began to blur a few years ago when several astronomers, including David Jewitt of the University of Hawaii at Manoa in Honolulu and Henry Hsieh, now at Queen's University Belfast, noticed that three known asteroids had sprouted dusty tails, just like comets.

Now, detailed simulations of the environment and evolution of these three asteroids - now considered hybrid bodies - and new observations of the composition of another asteroid are further eroding the differences between asteroids and comets.

Researchers presented the findings on July 16 at the Asteroids, Comets, Meteors meeting in Baltimore.

All three of the objects, dubbed main-belt comets or icy asteroids, have circular orbits that lie in the same plane in which the planets orbit the sun, just as ordinary asteroids do. That's an indication that the objects formed where they now reside, in the asteroid belt, the band of rocky material between the orbits of Mars and Jupiter, rather than emigrating from either of two frozen reservoirs of comets that lie at the fringes of the solar system, says theorist Nader Haghighipour of the University of Hawaii at Manoa.

"It is probable that the main-belt comets represent a new comet class in the solar system, one located unexpectedly close to the sun and revealing a previously unsuspected reservoir of ice nearby," says Jewitt.

As a comet approaches the sun, the ice on its surface suddenly converts from solid to gas (a process called sublimation). This change drags out dust as the ice vents into space, supplying the force that drives comets. However, most of the asteroid belt is now too warm for ice to remain stable on the surface of any of its denizens.

Haghighipour and Jewitt suggest that early in the solar system, the asteroid belt was cooler, and they note that the sun didn't produce quite as much heat when it was very young. More importantly, some of the sun's radiation was absorbed by the much larger population of dusty debris floating around the belt during those formative years, which would have given icy objects a chance to form there. As the asteroid belt heated up, surface ice would have melted, but pockets of ice just beneath and insulated by a cover of dirt or rock could have endured.

New simulations by Haghighipour show that collisions between these ice-laden asteroids and smaller bodies common in the asteroid belt can readily knock off the surface dirt and expose the hidden ice. Then, the next time one of these icy asteroids nears the sun: Voilà! It turns into a comet, replete with a dusty tail.

Two of the three main-belt comets lie within the Themis family of asteroids, and the third resides just outside that group. At the meeting, Andy Rivkin of the Johns Hopkins University's Applied Physics Laboratory in Laurel, Md., reported the first evidence that another family member, 24 Themis, not known to have a tail, has water ice on its surface. The new observations confirm that "sublimation of ice is the only real possibility for driving cometary activity in these Themis family objects," says Rivkin.

Impact Earth: Could we divert a giant asteroid?

Steve Connor
The Independent
Wed, 02 Jul 2008 04:16 EDT

A century ago this week, an asteroid fireball exploded over Siberia with the power of 185 Hiroshima bombs. Steve Connor asks how we can prevent a similar catastrophe in a major world city

A hundred years ago this week a man was sitting in the wooden porch of a trading post in the village of Vanavara in deepest Siberia when a blinding flash of light, followed by a huge blast of sound threw him to the ground.

Several years later, he recounted the terrifying moment to an inquisitive Russian scientist from St Petersburg who was on an expedition to find out what had caused such a massive explosion in one of the remotest regions on Earth.

©Alamy

The man's story turned out to be the first confirmed, eye-witness account of the extraordinary explosion caused when a large object from space explodes violently in the air above the ground after striking the Earth's atmosphere. "Suddenly, in the north sky... the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire," the man told the scientist. "There was a bang in the sky and a mighty crash... The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled," he said.

The heat from the blast was so intense the man thought that his shirt was on fire. The light from the explosion, and sunlight subsequently reflected in the atmospheric dust, could be seen for miles around. People as far away as London said that the night sky was so unusually bright that it was possible to read a newspaper in their gardens at midnight. The blast felled some 80 million trees over an area of 800 square miles.

If the asteroid had collided just a few hours later, or had come in on a slightly different trajectory, it could easily have exploded over Paris, London, New York or Moscow, with devastating consequences. Scientists calculate that if something of similar size exploded over London today, little within the M25 would remain standing. It would be as if a large thermonuclear bomb equivalent to 20 million tons of high explosives had been set off in the heart of the city.

What happened at about 7am on 30 June 1908, near the Podkamennaya Tunguska River in Siberia is now legendary among scientists studying near-Earth objects - asteroids and comets with orbits around the Sun that can bring them perilously close to our own planet. The Tunguska Impact is a stark reminder that, within living memory, a large enough object from space has hit the Earth on a latitude that could kill millions of people.

"If you want to start a conversation with anyone in the asteroid business, all you have to say is 'Tunguska'," says Don Yeomans, manager of the Near-Earth Object Office at NASA's Jet Propulsion Laboratory in Pasadena, California. "It is the only entry of a larger meteoroid we have in the modern era with first-hand accounts."

Although the impact happened in 1908, it was not until 1921 that Leonid Kulik, the chief curator of meteorites at St Petersburg Museum, led the first expedition to find out what happened, and possibly discover the crater it had left behind. He failed on that occasion because of the harsh conditions - swampy, mosquito-infested forests in summer and penetrating cold and ice in winter. In 1927, Kulik made another attempt and managed to reach the blast area to witness the devastation. He tried to get the deeply suspicious locals - reindeer herders called the Evenki - to tell him what they remember of that fateful morning 19 years earlier. They were reluctant, but he did manage to speak to the man at Vanavara, about 40 miles away from the blast's epicentre.

"At first, the locals were reluctant to tell Kulik about the event. They believed the blast was a visitation by the god Ogdy, who had cursed the area by smashing trees and killing animals. Those trees acted as markers, pointing directly away from the blast's epicentre. Later, when the team arrived at ground zero, they found the trees there standing upright - but their limbs and bark had been stripped away. They looked like a forest of telephone poles," says Dr Yeomans.

Kulik failed to find the impact crater, or any sign of the meteoroid itself. But the radial pattern of the felled timber, and in particular the central stand of trees stripped of branches, hinted at something else - that the blast wave had come from directly overhead and radiated out. In other words, instead of smashing into the ground, the object had disintegrated high overhead. Such an air burst causes the branches of trees directly below to be stripped off, leaving the trunks standing - as they did at Hiroshima.

The absence of a crater and of meteoroid fragments has led to wild speculation about what may have caused the explosion - from mini black holes to space aliens. A more sensible suggestion, however, is that it was not a space object, but an explosion caused by the sudden release of huge quantities of methane or some other kind of explosive gas from deep below the ground. But Dr Yeomans, along with most other experts, dismisses this "earth-belch" idea as implausible.

"A century later, some still debate the cause and come up with different scenarios that could have caused the explosion. But the generally agreed-upon theory is that on the morning of 30 June 1908, a large space rock about 120 feet across entered the atmosphere of Siberia and then detonated in the sky," Dr Yeomans says.

Such a rock would have been travelling at about 33,500mph as it plunged into the upper atmosphere. Friction with air molecules would have raised the temperature of the surrounding air to something like 25,000C. At about 28,000 feet, the pressure and heat would have cause the rock to explode into a fireball, releasing energy equivalent to about 185 Hiroshima bombs, according to Dr Yeomans. "That is why there is no impact crater. The great majority of the asteroid was consumed in the explosion."

Not all scientists agree with the details of this scenario. Giuseppe Longo of Bologna University and colleagues believe they have located a potential crater, a large water-filled depression known as Lake Cheko, where the meteoroid hit and was buried under permafrost. They intend to dig for what remains of the space object to prove their case. However, others point out that Lake Cheko lacks the attributes of a crater - such as raised edges - and is probably nothing more than one of the region's many oxbow lakes, formed from a river bend that collects slow-running water that then sinks into the permafrost below.

The really big question about Tunguska is how likely it is that something similar or worse will happen again? Asteroid experts have calculated that something the size of the object that hit Tunguska would strike the Earth at an average rate of one every 300 years. This does not mean that we can expect one in 200 years' time, only that, over a long period, they happen with a typical frequency of one every 300 years. It could happen tomorrow, or in several hundred years' time.

But as bad as a Tunguska would be over a heavily populated area, there are far more frightening scenarios. A larger object that hits the ground or ocean would cause more devastation by flinging debris into the air, or causing a tsunami. These sorts of objects are estimated to hit the Earth with a frequency of greater than once in every 1,000 years.

But their impact would be dwarfed by even bigger objects between 1km and 10km wide. These have struck the Earth in the past with devastating consequences. One such object is believed to have hit the Earth 65 million years ago, throwing up so much debris that it created a "nuclear winter" that cut out sunlight for several seasons, causing the famous mass extinction that led to the demise of the dinosaurs.

Dr Yeomans is part of a band of scientists lobbying for more research to investigate the orbits of the near-Earth objects that could pose a threat.With enough warning of an asteroid heading our way, it may be possible to deflect it if it appears to be on a collision course. Such surveys are under way. "We're identifying problems and hope to be able to do something about it," says Dr Yeomans.

NASA hopes to identify and track 90 per cent of all hazardous objects greater than 450 feet in diameter by the end of 2020. Scientists say that if ever a large object is discovered on a collision course with Earth, it might be possible to send up a nuclear-tipped rocket to blast it off course. A safer way would be to nudge it aside with smaller impacts, or even a "space sail" that uses the solar wind.

One of the lessons from Tunguska is that, although we are vulnerable to the threat, it is not something that should turn us to despair - such massive impacts are rare. As Dr Yeomans says: "I think about Tunguska all the time from a scientific point of view, but the thought of another Tunguska does not keep me up at night."

What are asteroids?

* Asteroids are chunks of rock or space debris left over from the birth of the solar system. The biggest is known as Ceres, which is 567 miles wide. Comets are "dirty snowballs" composed of ice and dust - they are less likely to hit the Earth than asteroids.

* Asteroid 2007 TU24 passed within 334,000 miles of Earth on 29 January 2008. At 800 feet wide, it was big enough to have caused global devastation if it had hit us.

* Asteroids larger than 160 feet wide are big enough to survive the journey through the Earth's atmosphere and hit the ground, causing further devastation as they throw debris into the air.

* Britain and the US are taking the issue seriously. The US Government has a near-Earth object survey Act and the UK has its own task force on potentially hazardous near-Earth objects.

Comment: For a more realistic idea of the probability of the Earth being struck by comets and other objects, be sure to read the sott Comets and Catastrophe series.

Forget the meltdown, worry about goo and asteroids

John Kay
The Financial Times
Wed, 09 Jul 2008 16:13 EDT

Last week was the 100th anniversary of the Tunguska explosion in Siberia. If you weren't celebrating, you should have been. The incident was probably the nearest we have come to extinction in modern human history - and we survived.

A large object - presumably an asteroid or meteorite - collided with the Earth. If it had landed in Manhattan, it would have destroyed New York. A bit bigger, and it would have been calamitous wherever it landed. A similar event at Yucatan, 65m years ago, wiped out the dinosaurs and most other species. It would have wiped us out too had we been there. We survived Tunguska because the impact was not too large.

There are many catastrophes graver than meltdown in the markets. The road to oblivion has many branches and unexpected turnings. Environmental catastrophes, like meteorites or seismic events, may do us in. Something even more devastating than the Yucatan object is on its way, but it may be tens of millions of years before it reaches us. Two hundred million years before Yucatan, the Permian extinction was even more devastating. We do not know the cause. It may have been a meteorite, but another theory blames the "clathrate gun", a massive release of methane from the ocean floor. Global warming could cause large methane release from permafrost or trigger another shot from the clathrate gun. But the environmental damage that humans cause is modest relative to the damage the environment can impose on itself.

Many other potential apocalypses are of our own making. The Frankenstein problem of technology run amok is beloved by science fiction writers. The world may be taken over by man-made objects, like robots, or mutations, like triffids. It may be submerged in grey goo from nanotechnology. The fiction genre survives because no one can say categorically that any of these things are impossible.

Madmen have always been a threat to humanity and technological advance increases their capacity to do damage. Three individuals - Hitler, Stalin and Mao - bear direct responsibility for the deaths of 30m or more people. Hitler might have destroyed the world if he had had the means.

The influenza pandemic of 1918-19 was, with Aids, the most devastating plague of modern times. But the Black Death killed 30 per cent of Europe's population. Still, 70 per cent of our ancestors survived and therefore we do also. We may not always be so lucky. A mutant virus may wipe out humankind and leave the world to less sociable species. The spread of the Black Death across Europe took years, but airlines could today carry the disease everywhere within hours.

Martin Rees, who engages with a litany of catastrophes, gave his book the provocative title of Our Final Century? But while technology causes many problems, it also fixes many. The Black Death was probably bubonic plague and if so we could now cure it. Even the asteroid can be deflected if we see it coming.

It is difficult to think about these issues in a dispassionate way. In his book Catastrophes, Richard Posner - an American legal scholar who loves economics more than most economists - proposes a cost/benefit analysis of all possible disasters. But the attempts to model the end of the world are mostly bogus. We have good data on frequencies of near-Earth objects but there is no meaningful way to attach probabilities to these other calamities.

The best way of dealing with grave uncertainties, as with more banal disasters, is to buy options against them. For each potential catastrophe, we should undertake research to ascertain what we might do if a remote possibility becomes a plausible reality. Instead, we talk endlessly about less dangerous issues that give more scope for moral and political posturing. Speeches about man-made environmental damage and terrorism arouse audiences, but asteroids and grey goo elicit only a chuckle. Our actions against more catastrophic threats are few, ineffectual and sometimes counterproductive.

In the meantime, mark February 1 2019 and April 13 2029 in your diaries. These are the next dates on which a very large object from space may land on your head.

Comment: Maybe the current financial crisis is manufactured in order to focus people's attention on "down to Earth" matters and away from the sky, where a greater threat lurks?

New Zealand: West Coast meteor may have landed

NZPA
Thu, 10 Jul 2008 13:16 EDT

The mystery of lights spotted off the west coast of New Zealand overnight has taken a twist with Punakaiki residents reporting a large bang and jolt.

Christchurch police received reports from Hokitika to Nelson of a light in the sky between 11pm and midnight, and Wanganui police received three calls of a bright light out at sea.

Wanganui police initially thought it was a flare but then reports came in from farther afield.

There were no reports of anything hitting the ground and a meteor is suspected.

But Les Wright, a resident of Punakaiki, a coastal settlement north of Greymouth, said he heard a rumbling sound followed by a loud thump as if something had hit the ground at about 8pm, which is about three hours before the lights were seen.

"There was one big jolt and then a smaller one. It was like an earthquake but not really," he said.

Prue Grant who lives on the beach at Punakaiki, also heard the noise.

"There was a huge bang, then a shake," she said.

Barrytown resident Sandy Passant saw red lights in the sky about 11pm. She also heard a noise at 8pm, and her partner Russell went outside to investigate but could not find anything.

"It was a very strange bang. We thought it might have been an earthquake but it was different -- just a big bang."

Canterbury University Mount John Observatory superintendent Alan Gilmore said he believed the thud was unrelated to the meteor at 11pm.

Gerry Lonie was on a fishing vessel near Hokitika and saw a meteor at 11pm.

"But there was a better one the night before -- there's been a few of them. It looked like a shooting star, it was quite a big flash but I didn't hear anything."

Constable Sean Judd, of Westport police, said he saw a light like a "very large, close up shooting star" just before 11pm. It lasted about three to four seconds before burning out.

"It was a white-green colour."

Asteroids and Comets: The Earth's Scars

Richard Stone
National Geographic
Tue, 15 Jul 2008 20:26 EDT

©Stephen Alvarez

Asteroids and comets in nearby space pose a constant threat to our planet. Can we avert catastrophe the next time around?

The first sign of the threat was no more than a speck on a star-streaked telescope image. Just after 9 p.m. on June 18, 2004, as twilight faded over Kitt Peak National Observatory in Arizona, David Tholen was scanning for asteroids in an astronomical blind spot: right inside Earth's orbit, where the sun's glare can overwhelm telescopes. Tholen, an astronomer from the University of Hawaii, knew that objects lurking there could sometimes veer toward Earth. He had enlisted Roy Tucker, an engineer and friend, and Fabrizio Bernardi, a young colleague at Hawaii, to help. As they stared at a computer, three shots of the same swath of sky, made a few minutes apart, cycled onto the screen. "Here's your guy," said Tucker, pointing at a clump of white pixels that moved from frame to frame.

Tholen reported the sighting to the International Astronomical Union's Minor Planet Center, a clearinghouse for data on asteroids and comets. He and Tucker hoped to take another look later that week, but they were rained out, and then the asteroid disappeared from view.

When astronomers got a fix on it again that December, they realized they had a problem. The rock, bigger than a sports arena, tumbles menacingly close to our planet every few years. As observations streamed into the Minor Planet Center, the asteroid, named Apophis after the Egyptian god of evil, looked increasingly sinister. "The impact hazard kept getting higher and higher," says Tholen. By Christmas, models predicted 1-in-40 odds that Apophis would smash into Earth on April 13, 2029, and a ripple of alarm spread to the public. "One colleague called it the grinch that stole Christmas," Tholen says.

Then on December 26, 2004, a real catastrophe struck: the Indian Ocean tsunami, which claimed hundreds of thousands of lives. The public forgot about Apophis. In the meantime, astronomers had dug out earlier images of the asteroid. The extra data enabled the scientists to calculate its orbit, and they discovered that it would actually whiz safely by Earth in 2029. But they could not rule out a slender chance that Apophis would strike with catastrophic effect its next time around, on Easter Sunday, 2036.

An estimated ten million rocky asteroids and ice-and-dirt comets pirouette in outer space, and once in a while their paths fatefully intersect our planet's. One such encounter took place a hundred miles from present-day Washington, D.C., where a 53-mile-wide crater lies buried beneath Chesapeake Bay - the scar left when a two-mile-wide rock smashed into the seafloor 35 million years ago. More notorious is the titan, six miles in diameter, that barreled into the Gulf of Mexico around 65 million years ago, releasing thousands of times more energy than all the nuclear weapons on the planet combined. "The whole Earth burned that day," says Ed Lu, a physicist and former astronaut. Three-quarters of all life-forms, including the dinosaurs, went extinct.

Astronomers have identified several hundred asteroids big enough to cause a planetwide disaster. None is on course to do so in our lifetimes. But the heavens teem with smaller, far more numerous asteroids that could strike in the near future, with devastating effects. On June 30, 1908, an object the size of a 15-story building fell in a remote part of Siberia called Tunguska. The object - an asteroid or a small comet - exploded a few miles before impact, scorching and blowing down trees across 800 square miles. The night sky was so bright with dust from the explosion, or icy clouds from the water vapor it blasted into the upper atmosphere, that for days people in Europe could read newspapers outdoors at night. On Tunguska's hundredth anniversary, it's unsettling to note that objects this size crash into Earth every few centuries or so.

The next time the sky falls, we may be taken by surprise. The vast majority of these smallish bodies, capable of wiping a city off the map, are not yet on our radar screens. "Ignorance is bliss, in that if you don't know about these things, you just go about your merry way," says Lu. Over the next decade, however, sky surveys like Tholen's should begin filling that gap, cataloging asteroids by the thousands. "Every couple of weeks," says Lu, "we're going to be finding another asteroid with like a one-in-a-thousand chance of hitting the Earth."

The goal is not just to foretell the date and time of a potential catastrophe. The goal is to forestall it. With years or decades of warning, a spacecraft, using its own minuscule gravity, might nudge a threatening asteroid off course. For objects requiring a bigger kick, a kamikaze spacecraft or a nuclear bomb might do the job. Vexing dilemmas would attend this showdown in space. How will governments decide to act? "This is a class of problem that the world isn't set up to deal with," says physicist David Dearborn, an advocate of a nuclear strike against an incoming asteroid.

Two facts are clear: Whether in 10 years or 500, a day of reckoning is inevitable. More heartening, for the first time ever we have the means to prevent a natural disaster of epic proportions.

Every day, dozens of tons of detritus from outer space - dust from comets, tiny shards of asteroids - burn up in the Earth's upper atmosphere, leaving bright meteor trails at night. Most days a chunk or two of rock or metal, fist size or bigger, survives the fiery plunge.

Yet the odds of seeing a meteorite hit the ground, let alone being struck, are phenomenally low. Only one is known to have hit a person. Around 1 p.m. on November 30, 1954, a meteorite tore through the roof of a house near Sylacauga, Alabama, across the street from the Comet Drive-in Theatre. The rock, about the size of a softball, caromed off a console radio and clipped Ann Hodges as she snoozed on her couch, bruising her left hip and wrist. She was hospitalized to recover from the shock.

Since then, there have been some spectacular near misses. On August 10, 1972, an object around 15 feet across and weighing 150 tons skipped off the upper atmosphere. Hundreds of eyewitnesses saw the glowing streak, dazzling on a sunny afternoon, as it traversed the sky from Utah to Alberta before whizzing back out into space. On March 22, 1989, a rock as much as a thousand feet across came within a few hundred thousand miles of Earth - an uncomfortably close shave.

Erosion and vegetation have erased most of the scars left by impacts in the geologic past. Perhaps the best preserved lies about half an hour east of Flagstaff, Arizona. On a late autumn morning Carolyn Shoemaker and I pull off Interstate 40 and wind through scrubby desert toward a low rise marking the rim of the crater. Fifty thousand years ago this was a forested plain inhabited by mammoths, giant ground sloths, and other Ice Age animals. Shoemaker, an asteroid expert with the Lowell Observatory in Flagstaff, imagines the day the sky fell. "Suddenly, there's a terrific, brilliant light," she says. In a flash, a searing-hot iron-nickel mass, 150 feet wide and weighing 300,000 tons, tears into the Coconino sandstone, flinging boulders and molten iron for miles. A blast of wind more powerful than any earthly tornado scours the landscape.

All that's left of the cataclysm now is a chasm three-fourths of a mile wide and 570 feet deep, fringed with Mormon tea bushes. At the turn of the 20th century, an engineer named Daniel Moreau Barringer was convinced that a massive iron meteorite lay beneath the crater and obtained the mining rights to the land. But after a series of shafts revealed nothing, many prominent geologists concluded that a volcanic eruption, not a meteorite, had formed the crater.

Carolyn's husband, Gene, made Meteor Crater one of America's most recognizable landmarks. In the late 1950s he mapped the overturned rock around the crater and pointed out similarities to the Teapot Ess crater in Nevada, formed by a nuclear test. His data showed that Barringer was right: A meteorite had gouged the crater, although most of the iron had melted into tiny droplets. Several of Barringer's shafts can still be seen from the rim, along with a full-size cutout of a waving astronaut - a nod to NASA, which once used the crater as a training ground. Some visitors whisper and point at Carolyn, and one man plucks up the courage to come over and request her autograph. Carolyn is famous in her own right. She discovered a comet that, in 1994, vividly demonstrated the cosmic threat we face.

In 1980, their children grown and out the door, Gene suggested that Carolyn start a career as an asteroid hunter. "I'm a morning person," she says. "I had never stayed awake all night in my life. I didn't know if I could do that." But she decided to give asteroid hunting a shot. Gene had access to the Palomar Observatory near San Diego. "After a couple years, I learned how to discover things," she says, modestly. She has 32 comets and 367 asteroids to her credit. "Some are more interesting than others."

On March 25, 1993, Carolyn, Gene, and David Levy, an amateur astronomer, were at Palomar for their scheduled observation time. Snow was falling, and the night promised to be long and boring. Carolyn killed time by studying a batch of overexposed film from the previous night. Many frames were worthless. On one of the last images, however, she came across a smudge. "I said, 'It looks like a squashed comet.' " The team asked astronomers at Kitt Peak to take a look. It then occurred to Carolyn that her squashed comet might be a broken comet. Confirmation came that same night when Kitt Peak spotted a string of comet shards traveling together.

Other astronomers soon counted some two dozen pieces of comet Shoemaker-Levy 9 and worked out its strange history and fate. In July 1992, it seemed, the comet had swung so close to Jupiter that the giant's massive gravity had torn it apart. Now the remnants, some of them hundreds of feet wide, were destined to collide with Jupiter in July 1994. When the time came, most of the world's astronomers were watching.

The impacts took place on Jupiter's far side, out of sight of Earth, but the blows sent superheated gas billowing far above the atmosphere. The largest unleashed shock waves that roiled an area at least three times the width of Earth. "It was pretty awesome," Carolyn says. The Shoemakers basked in the glow of their discovery. Then tragedy struck. In 1997 they were in a head-on car crash in the Australian outback. Gene died at the scene. An ounce of his ashes traveled to the moon with NASA's Lunar Prospector spacecraft.

Carolyn scattered the rest at Meteor Crater.

If the Shoemakers' namesake or the monster that annihilated the dinosaurs were bearing down on us, there would be little we could do. For every planet killer, however, there are thousands of smaller asteroids and comets - up to a mile or so across - that could conceivably be deflected. First we'd have to see them coming.

In 1998 the U.S. Congress ordered NASA to identify at least 90 percent of the largest asteroids and comets in the inner solar system - objects six-tenths of a mile or more in diameter. To date, telescopes have pinpointed more than 700 out of an estimated population of 1,000. In 2005 Congress got more ambitious, directing the space agency to track down the far more numerous asteroids 460 feet or more in diameter - still big enough to take out a city or state.

A new telescope is about to begin scanning the sky for these dim, elusive objects. From a peak on Maui, the Panoramic Survey Telescope and Rapid Response System, or Pan-STARRS, will scrutinize the night sky with a 1.4-billion-pixel camera that produces images so detailed a single one, if printed, would cover half a basketball court. Computers will scan the data, flagging statistical curiosities that astronomers can check the old-fashioned way, by taking a look. The Maui telescope is just a prototype; ultimately, Pan-STARRS will include an array of four cameras. "We'll have catalogs of all the things that go bump in the night," says Ken Chambers of the University of Hawaii, including perhaps 10,000 potentially hazardous asteroids.

Within decades, the world's leaders may be forced to grapple with a momentous decision: whether and how to deflect an incoming object. Few experts are giving this much thought, says astronomer David Morrison of NASA's Ames Research Center: "The number would roughly staff a couple shifts at a McDonald's."

Lu, the former astronaut, is one. Now an executive at Google, he is helping design a massive database for a successor to Pan-STARRS, the Large Synoptic Survey Telescope, which will scrutinize the sky in even more detail starting in 2014. Lu is also the coauthor of a scheme for using a spacecraft to coax an earthbound asteroid off its dangerous path. "We were originally thinking about how you would land on an asteroid and push it," he says. "But that doesn't work well." If the surface is crumbly, the lander might skid off. Moreover, asteroids twirl through space. "If you're pushing and the thing is rotating, the pushing just cancels out," Lu says.

Then he and Stanley Love, a fellow astronaut, realized pulling would be much easier. A spacecraft could hover nearby and fire its thrusters, gently tugging the asteroid along. No harpooning or lassoing would be required. "Rather than having a physical line between you and the thing you're towing, you're just using the force of gravity between them," Lu says. The "gravity tractor" would tug the asteroid off course at a mere fraction of a mile an hour. But this subtle shift, magnified over the vastness of space, could mean missing Earth by tens of thousands of miles.

Lu's scheme would work only for asteroids up to a few hundred yards across that could be engaged far from Earth. If a small rock sneaks up on us, we could try ramming it with a spacecraft. But there's a drawback, says Morrison: "If you hit an asteroid with enough energy to break it apart, but not necessarily enough energy to disperse it widely, you now have a flying collection of stuff. You have to ask how practical that is." When all else fails, and for large asteroids and comets, only one strategy has a chance of working: We'll have to bomb them back to the Stone Age.

Stands of frosted firs and white birch cluster along the highway leading southwest from Yekaterinburg, the city in the Ural Mountains where Russia's last tsar, Nicholas II, and his family were murdered 90 years ago. Under a dull sun, fishermen huddle over holes on a frozen lake, floppy-eared fur hats hiding their faces. A road with a misspelled signpost for a tiny village marks the turnoff for the formerly secret city of Snezhinsk, code-named Chelyabinsk-70 during the Cold War. Snezhinsk is home to one of Russia's two main nuclear weapons laboratories. After the collapse of the Soviet Union, it fell on hard times; ten years ago, with Russia's economy in shambles, staff salaries went unpaid, and the director committed suicide.

Nowadays, with Russia prospering, the laboratory is humming with top secret work. Obtaining permission to enter proved impossible. But Vadim Simonenko, the deputy scientific director, and experimentalist Nikolay Voloshin agreed to meet at a sanatorium in nearby Dalnyaya Dacha. In a cool, dim, and empty dining hall, Voloshin opens a bottle of cognac, and over salmon canapés, cold cuts, and sliced cucumbers, the two weapons scientists discuss how their bombs could save the world.

If Edward Teller is the father of the hydrogen bomb, Simonenko is the father of the asteroid bomb. In the mid-1960s the superpowers dreamed of using their nuclear arsenals for peaceful purposes, such as leveling mountains and digging canals. Simonenko, a new recruit to the lab, was asked to study the effects of a torpedo-shaped charge that would explode laterally, ideal for earthmoving. It occurred to him that such a device could also be used to deflect an object in space. He told his boss, who laughed and ordered the eager young physicist to get back to work.

Though nuclear excavation never became a reality, Simonenko went on studying nuclear asteroid deflection. He and Voloshin concluded that the best way to deflect an asteroid up to a mile or so wide would be to detonate a nuclear charge nearby. The intense radiation would fry the surface, driving off a "sacrificial layer" of rock. The expanding vapor would act as a rocket motor, nudging the asteroid onto a new trajectory. For a smaller, Tunguska-size rock, Simonenko says, "it would be simpler: We vaporize it."

Simonenko has a brother-in-arms in nuclear physicist David Dearborn of Lawrence Livermore National Laboratory in northern California. Dearborn's day job is determining whether the aging weapons in the U.S. nuclear stockpile are reliable. In his spare time, he ponders asteroid defense. He, too, favors a standoff nuclear blast. "Not too close - then the blast is too intense, and things shatter too much. And not too far, or you don't get enough energy."

Although it may be technically straightforward to dust off a few warheads and sling them at an asteroid, deciding whether to press the red button - and which nation gets to press it - could be excruciating. First, the nation with its finger on the trigger would have to withdraw from the Outer Space Treaty, which bans the use of nuclear weapons in space. But if catastrophe looms, says Dearborn, "people would really have to say, 'Can we be brighter than the dinosaurs?'"

Apophis may pose the first real test of our collective intelligence. For now, scientists can give only a range of probabilities for its future trajectory. As it swings past Earth in 2029, ducking under dozens of high-flying communications and spy satellites and appearing as a bright star lumbering across the night skies over Europe, there's a slim chance that Apophis will pass through a "keyhole." In this narrow corridor of space, maybe a few hundred yards wide, Earth's gravity would deflect the asteroid just enough to put it on a certain collision course with our planet on the next pass, in 2036. The odds that Apophis will pass through this fatal corridor are currently estimated at 1 in 45,000. Continued tracking will almost certainly deliver an all clear a few years from now. If not, we might have to wait until weeks after its close approach in 2029 to learn whether Apophis has squeezed through a keyhole, leaving us precious little time to avert calamity in 2036.

In the prophesies of the Hopi of the American Southwest, the arrival of a spirit called Yellow Star Kachina will herald the end of the world. When Hopi elders heard about Apophis in 2004, they worried that Yellow Star Kachina was on its way. Carolyn Shoemaker tried to reassure them that it was not.

Let's hope she was right.

Comment: The threat to Earth by asteroids and comet fragments has been increasing dramatically, please see our 'must-read' Comet Series for more information.

Chile: Meteorite trail surprises Punta Arenas and Tierra del Fuego

Merco Press
Fri, 18 Jul 2008 15:36 EDT

It is almost confirmed that the bright flash seen last Monday night in great parts of Magallaes region, included Tierra del Fuego in the extreme south of Chile was a meteorite.

Residents throughout the region: in Punta Arenas, Puerto Natales and in Tierra del Fuego Porvenir recall seeing at approximately 10:30 p.m. a bright flash in the night sky. Witnesses then heard a loud crack, presumably the result of the meteorite breaking the sound barrier as it passed over the region, reported the local press.

The head of the Punta Arenas Airport, Jan Carlo Onetto, confirmed that the unidentified flying object was not of human origin.

"In the four years I've lived in the area, the radars have never before detected something that wasn't a plane," he said. "I think it was a meteorite that entered the zone at high speed and broke the sound barrier, thus producing the loud crack. People are assuming it fell somewhere south of here. It may have fallen in the Straights (of Magellan) or further south."

Onetto's theory was corroborated by Chilean Antarctic Institute scientist Stefan Kraus, who told Radio Polar that the object was likely a "stony" meteorite, the most common type. "All the data collected and the observations so far, confirm it", he added.

"The fire ball, the stellar trail and the loud sound which was reported are typical of this kind of phenomenon in any part of the world; so we can say it was a meteorite", said Krauss who nevertheless pointed out it would very difficult to trace any tiny rests on the soil and if so, "it would be extremely lucky".

"Tiny pieces must have spread over miles of open range, many kilometers from Punta Arenas and in unpopulated areas of Patagonia", said Krauss.

10 Greatest Major-Impact Craters on Earth (photo)

Environmental Graffiti
Fri, 18 Jul 2008 17:03 EDT

©Unknown

Imagine staring into the sky and seeing a tiny yellow dot, gradually getting closer. That dot doubles in size every second, until it slowly darkens the sky. You realize that this dot is actually the size of New York City and is screeching through the atmosphere faster than the speed of sound, coming right for you. This massive object will cause tsunamis, earthquakes and obliterate natural daylight for years...oh... and it will kill you. Similar asteroid impacts have and will happen on numerous occasions in our earth's history. Today we'll show you the biggest impact craters by diameter.

10. Barringer Crater, Arizona, US

©Unknown

Some 49,000 years ago a large nickel-iron meteorite "just" 150 ft across, weighing several hundred thousand tons (~300,000) and traveling at a speed of 40,000 miles per hour, hit Earth. The result of this meteor lies 55 km east of Flagstaff, Arizona and is called the Barringer Crater: the best preserved impact crater ever. The force generated by the impact was equal to the explosion of 20 million tons of TNT. Picture that.

It measures 0.75 miles (1.2 km) across, is 575 ft (175 m) deep and has a rim 148 ft (45 m) higher than the surrounding plain. Discovered in 1902, the Barringer Crater was named after Daniel Barringer, a successful mining engineer. Today it is still owned by his family and is also known as Meteor Crater, Coon Butte, and Canyon Diablo.

9. Bosumtwi, Ghana

©Unknown

About 30 km south-east of Kumasi, Ghana, in the crystalline bedrock of the West African Shield, lies Lake Bosumtwi: the country's only natural lake. The impact of a meteorite some 1.3 million years ago, opened up hole in the ground with a 6 mile (10.5 km) diameter. The crater gradually got filled with water to form the lake we see today. Surrounded by dense rainforest, the Ashanti people consider it to be sacred. They think it's the place where souls of the dead come to bid farewell to the god Twi.

8. Deep Bay, Canada

©Ersi

Situated near the south-western tip of Reindeer Lake in Saskatchewan, Canada, Deep Bay is a strikingly circular, very deep and unusually irregular and shallow lake. The 8 mile (13km) wide crater is a complex impact structure with a low, totally submerged central uplift, formed about 100 million years ago (some say 140 million) when a large meteorite crashed in the area.

7. Aorounga impact crater, Chad

©Unknown

Aorounga is an eroded meteorite impact crater that formed 2-300 million years ago in an area of the Sahara Desert, northern Chad, in Africa, when a comet or asteroid with a 1 mile diameter (1.6 km across) hit the crust of Earth. Such impacts only happen roughly, once every million years.

The crater is about 11 miles (17 km) across and is accompanied by two nearby circular features that have been revealed by the Space Shuttle's SIR-C radar after picturing an area of about 22 miles (36 km). If the assumptions and the hypothesis that the dark band in the upper right corner could be a second impact crater, then Aorounga may be part of a chain of multiple impact craters.

6. Gosses Bluff, Australia

©Unknown

Approximately 142 million years ago, a large asteroid or comet (22 km in diameter) crashed at 40 km/sec in the southern Northern Territory, near the center of Australia, and released massive energy equivalent to 22 000 megatonnes of TNT. This is how one of the most significant impact structures in the world, the Gosses Bluff crater formed. Dimensions are also impressive: it has a 15 mile (24km) diameter and goes down to 16,400 ft (5,000m). What we get to see today is a highly eroded structure that still stands as a stark reminder of the event.

5. Mistastin Lake, Canada

©Unknown

Located in Labrador, Canada, the Mistastin crater is the result of a meteorite crash, that caused a 17.4 miles (28km) wide giant hole into the ground, 38 million years ago. Since then the eastward moving glaciers have drastically reduced its size and a lake appeared within the rims, Mistastin Lake. It occupies an elliptical, east - north-east trending depression, approximately 11 by 7 miles in size. In the middle of the lake, there's an arcuate central island which could be the central uplift of the complex crater structure.

4. Clearwater lakes, Canada

©Unknown

Two circular lakes/impact craters on the Canadian Shield in Quebec formed simultaneously by the impact of an asteroid pair which crashed on Earth approximately 290 million years ago, near the eastern shore of Hudson Bay. The larger of the two craters is West Clearwater Lake with a 20 mile (32km) diameter while the smaller one, East Clearwater Lake has a 13.7 mile (22km) diameter. The lakes are a great tourist location mostly because of the number of sprinkling islands that form a sort of a "dotted line". The lakes are also, obviously, famous for their clear waters.

3. Kara-Kul, Tajikistan

©Unknown

At an altitude of 13,000 feet (3,900 m) above sea level, lies Kara-Kul, also known as Qarokul: a 16 mile (25km) wide lake in the Pamir Mountains in Tajikistan, close to the Chinese border. The lake is actually located within a 28 mile (45km) wide circular depression, which was hit by a meteorite approximately 5 million years ago, Kara-kul was only discovered recently, through satellite imagery.

2. Manicouagan, Canada

©Unknown

Manicouagan Reservoir (Lake Manicouagan) also known as the "eye of Quebec", is an annular lake in central Quebec, Canada, that lies within the remains of an ancient, eroded impact crater. Some 212 million years ago, a 3 mile (5km) wide asteroid hit the earth, to causing a 62 mile (100km) wide giant hole. It has been worn away by the passing of glaciers and other erosive processes, ever since.

1. Chicxulub, Mexico

©Unknown

Buried underneath the Yucatán Peninsula in Mexico, near the Chicxulub village (which means "the tail of the devil" in Mayan), this ancient impact crater is simply huge at 105 miles (170km) in diameter. The impact happened roughly 65 million years ago when a comet or asteroid the size of a small city crashed (equivalent to 100 teratons of TNT) on Earth and caused destructive mega-tsunamis, earthquakes and volcanic eruptions around the globe.

The Chicxulub impact is widely believed to have led to the extinction of dinosaurs, because of a global firestorm or because of a dramatic and widespread greenhouse effect that caused long-term environmental changes.

Lack of cracks may explain Peru meteorite mystery

Devin Powell
ScientistSpace
Thu, 03 Jul 2008 14:33 EDT

It's the Superman of space rocks. A mysterious meteorite that crashed to Earth last year may have been the toughest of its kind.

Comets and Asteroids - Learn more about the threat to human civilisation in our special report.

Tunguska catastrophe: Evidence of acid rain supports meteorite theory

Science Centric
Sat, 19 Jul 2008 18:17 EDT

The Tunguska catastrophe in 1908 evidently led to high levels of acid rain. This is the conclusion reached by Russian, Italian and German researchers based on the results of analyses of peat profiles taken from the disaster region.

In peat samples corresponded to 1908 permafrost boundary they found significantly higher levels of the heavy nitrogen and carbon isotopes 15N and 13C. The highest accumulation levels were measured in the areas at the epicentre of the explosion and along the trajectory of the cosmic body. Increased concentrations of iridium and nitrogen in the relevant peat layers support the theory that the isotope effects discovered are a consequence of the Tunguska catastrophe and are partly of cosmic origin. It is estimated that around 200,000 tons of nitrogen rained down on the Tunguska region in Siberia at that time. 'Extremely high temperatures occurred as the meteorite entered the atmosphere, during which the oxygen in the atmosphere reacted with nitrogen causing a build up of nitrogen oxides,' Natalia Kolesnikova told the Russian news agency RIA Novosti on last Monday. Mrs. Kolesnolova is one of the authors of a study by Lomonosov Moscow State University, the University of Bologna and the Helmholtz Centre for Environmental Research (UFZ), which was published in the journal Icarus in 2003.

The Tunguska event is regarded as one of the biggest natural disasters of modern times. On 30 June 1908 one or more explosions took place in the area close to the Tunguska River north of Lake Baikal. The explosion(s) flattened around 80 million trees over an area of more than 2000 square kilometres. The strength of the explosion is estimated to have been equivalent to between five and 30 megatons of TNT. That is more than a thousand times as powerful as the Hiroshima bomb. This almost unpopulated region of Siberia was first studied in 1927 by Professor Leonid A. Kulik. There are a number of different theories about what caused the catastrophe. However, the majority of scientists assume that it was caused by a cosmic event, such as the impact of a meteorite, asteroid or comet. If it had exploded in the atmosphere just under five hours later, St. Petersburg, which was the capital of Russia at that time, would have been completely destroyed because of the Earth's rotation.

In two expeditions in 1998 and 1999, Russian and Italian researchers took peat profiles from various locations within the Siberian disaster area. The type of moss studied, Sphagnum fuscum, is very common in the peat material and obtains its mineral nutrients exclusively from atmospheric aerosols, which means that it can store terrestrial and extraterrestrial dust. Afterwards, the samples were analysed in laboratories at the University of Bologna and the Helmholtz Centre for Environmental Research (UFZ) in Halle/Saale. Among other things, the UFZ specialises in isotope analyses of sediments, plants, soil and water and it was asked to help by the team of Moscow researchers led by Dr Evgeniy M. Kolesnikov. Kolesnikov, who has been investigating the Tunguska event for 20 years, has been to Leipzig University and UFZ twice as a guest researcher with the help of the German Research Foundation (DFG) to consult with the isotope experts. 'The levels of accumulation of the heavy carbon isotope 13C measured right on the 1908 permafrost boundary in several peat profiles from the disaster area cannot be explained by any terrestrial process. This suggests that the Tunguska catastrophe had a cosmic explanation and that we have found evidence of this material,' explains Dr Tatjana Boettger of the UFZ. Possible causes would be a C-type asteroid like 253 Mathilde, or a comet like Borelly.

Source: Helmholtz Association of German Research Centres

Strange object filmed in skies above Winnipeg

CTV News Staff
CTV.ca
Tue, 22 Jul 2008 20:59 EDT

Is it a comet, an aircraft, or satellite debris burning up in the atmosphere? A Winnipeg woman is asking for help to explain a mysterious object she caught on camera.

Image of a strange object seen in the sky over Winnipeg, Man. on Monday, July 21, 2008

"It was like a red fireball falling down from the sky," Sylvia McLeod, 31, told CTV.ca Tuesday.

"I have no idea what it is. I thought it would be all over the news. I went on the Internet and tried to find any information, but couldn't find anything."

McLeod said she filmed the strange object Monday night between 9:30 p.m. and 10:30 p.m., just as the sun set.

"It was moving kind of slowly. But I knew it was falling. I couldn't get the whole shot of it because my camera didn't have enough memory," she said.

Asked whether she had ever seen anything like it before, McLeod answered: "Only in movies."

Prof. Jaymie Matthews, of the Department of Physics and Astronomy at the University of British Columbia, said he wasn't sure exactly what was caught on camera -- but he ruled out several possibilities.

"A comet that bright, that close to the Sun, visible in the twilight sky, would have been spotted by professional and amateur astronomers long before last night," he wrote in an email from Paris. "And it would have been visible to people across North America last night, and still tonight."

He added that it was also definitely not a meteor, fireball or disintegrating space debris. "It would have moved across the sky or even below the horizon in the time covered by the video footage," he wrote.

Comment: Since there is no copy of the video available at this time to determine how fast it was moving, one cannot "definitely" rule out that is was not a meteor, fireball or disintegrating space debris either.

So what was it?

Chris Rutkowski, who has seen hundreds of strange unexplained images as director of the Winnipeg-based Ufology Research Institute, said his best guess would be a plane.

He said it would be "high enough that it's still in sunlight as the sun was setting," and the tail of the object would be the contrail of the aircraft -- the vapour trail left by the plane's engines.

The 2008 Perseid Meteor Shower

Physorg.com
Wed, 23 Jul 2008 03:49 EDT

©Unknown

"The time to look is during the dark hours before dawn on Tuesday, August 12th," says Bill Cooke of NASA's Meteoroid Environment Office at the Marshall Space Flight Center. "There should be plenty of meteors--perhaps one or two every minute."

The source of the shower is Comet Swift-Tuttle. Although the comet is far away, currently located beyond the orbit of Uranus, a trail of debris from the comet stretches all the way back to Earth. Crossing the trail in August, Earth will be pelted by specks of comet dust hitting the atmosphere at 132,000 mph. At that speed, even a flimsy speck of dust makes a vivid streak of light when it disintegrates--a meteor! Because, Swift-Tuttle's meteors streak out of the constellation Perseus, they are called "Perseids."

Serious meteor hunters will begin their watch early, on Monday evening, August 11th, around 9 pm when Perseus first rises in the northeast. This is the time to look for Perseid Earthgrazers--meteors that approach from the horizon and skim the atmosphere overhead like a stone skipping across the surface of a pond.

"Earthgrazers are long, slow and colorful; they are among the most beautiful of meteors," says Cooke. He cautions that an hour of watching may net only a few of these at most, but seeing even one can make the whole night worthwhile.

A warm summer night. Bright meteors skipping overhead. And the peak is yet to come. What could be better?

The answer lies halfway up the southern sky: Jupiter and the gibbous Moon converge on August 11th and 12th for a close encounter in the constellation Sagittarius: sky map. It's a grand sight visible even from light-polluted cities.

For a while the beautiful Moon will interfere with the Perseids, lunar glare wiping out all but the brightest meteors. Yin-yang. The situation reverses itself at 2 am on Tuesday morning, August 12th, when the Moon sets and leaves behind a dark sky for the Perseids. The shower will surge into the darkness, peppering the sky with dozens and perhaps hundreds of meteors until dawn.

For maximum effect, "get away from city lights," Cooke advises. The brightest Perseids can be seen from cities, he allows, but the greater flurry of faint, delicate meteors is visible only from the countryside. (Scouts, this is a good time to go camping.)

The Perseids are coming. Enjoy the show!

Small Satellite Designed to Spot Big Bad Asteroids

Jeremy Hsu
Space.com
Wed, 23 Jul 2008 18:43 EDT

©Unknown

A tiny Canadian satellite is gearing up for a mission to hunt wayward space rocks that may pose a threat to Earth.

Only the size of a suitcase, the Near Earth Object Surveillance Satellite (NEOSSat) has a 5.9-inch (15-cm) telescope and weighs about 143 pounds (65 kg). But it's designed to hunt for threatening space rocks from Earth orbit, where the telescope can avoid interference from the planet's atmosphere.

"That's why a small telescope in space can be a lot more comparable to a large telescope on the ground," said Alan Hildebrand, planetary scientist at the University of Calgary and head of the asteroid search project for NEOSSat.

The Canadian microsatellite would also keep an eye on Earth's satellite traffic for both U.S. and Canadian space commands, swiveling around to target space rocks and satellites hundreds of times a day. That requires a revolutionary turning system for the $12 million-satellite to do its job upon launch in early 2010.

Astronomers have particular interest in Near Earth Objects, because such objects might threaten Earth in the near or distant future. Nearby asteroids could likewise serve as targets for future spacecraft missions to investigate.

NEOSSat will also shed more light on the less famous Inner Earth Objects, or asteroids found close to the sun within Earth's orbit, mission managers said.

Point and click

NEOSSat draws upon the technological heritage of a star-gazing mission called MOST (Microvariability and Oscillation of STars), which represented Canada's first space telescope. But the newer microsatellite also boasts an attitude control system based on spinning reaction wheels that allow it to turn quickly without consuming rocket fuel.

"We have to be able to point precisely at a chunk of sky for 100 seconds," Hildebrand told SPACE.com. "Then you want to be able to slew from one field to another as fast as possible."

Such rapid response balances out with the need to keep the space telescope steady on its target, whether peering at rocks in the asteroid belt or tracking a moving satellite.

"The attitude-control system is an absolute must," said Brad Wallace, scientist at Defense Research Development Canada (DRDC), the agency working with the Canadian Space Agency on NEOSSat.

However, the system's reaction wheels don't require consumable fuel to do their work. NEOSSat will draw power from solar panels that convert the sun's energy into the required amount of electricity - just 45 watts, or less power than an average light bulb.

Let's go asteroid hunting

Low energy usage and a small size may make NEOSSat seem paltry compared to large ground telescopes that can cost $50 million and up. But scientists look forward to having a space telescope that can check out asteroids without bad weather or atmospheric background getting in the way.

"In terms of advantages of being in space, we've got 24/7 availability," Hildebrand said.

Ground telescopes face limits even with blue skies on Earth, because the atmosphere makes it harder to spot the faint light signals from asteroids. NEOSSat reduces the background interference to one tenth of that on Earth, by going up roughly 435 miles (700 km) above the atmosphere.

Hildebrand hopes the microsatellite to discover at least 100 Near Earth Objects per year once operational, and many more asteroids in the main asteroid belt between Mars and Jupiter.

Space traffic control

The microsatellite will also spend half its time tracking other satellites in orbit around Earth.

"Our first and foremost goal is to demonstrate satellite tracking capability," said Wallace, who leads the DRDC science team focused on traffic control.

Wallace's team will spend NEOSSat's first year testing new observing and tracking techniques, before handing over the keys to DRDC's client, the Canadian Forces. That would allow the space telescope to take a more active role in helping the North American Aerospace Defense Command (NORAD) monitor the skies.

Satellite tracking requires slightly less of the microsatellite's capabilities, but Wallace also plans to test it on scenarios such as tracking "lost" objects and doing hand-off coverage that picks up from where another telescope began.

NEOSSat's ability to take on dual responsibilities points to a future where microsatellites increasingly become the standard. The ability to use more recent technology and commercial, off-the-shelf parts has only sped up the miniaturization process, Wallace said.

Earth orbit will undoubtedly get more crowded not long after NEOSSat's 2010 debut - DRDC has already begun work on a second microsatellite that will monitor maritime shipping and travel on Earth.Asteroid Crash May Have Demagnified Mars

Irene Klotz
Discovery News
Thu, 24 Jul 2008 18:10 EDT

Scientists don't know what happened on Mars that caused its magnetic field to collapse. They suspect the planet's liquid metallic core cooled, ending convective currents that spread magnetic field lines through the planet's rock and soil and out into space.

©Unknown

Missing Magnetic Field

But that may just be part of the story.

A team of researchers led by Jafar Arkani-Hamed of the University of Toronto in Canada believe a large asteroid circling the planet set up a gravitational tug-of-war that got Mars' core churning. Eventually, the asteroid lost its grip and crashed into its parent planet. Mars paid a dear price as well. Without the tidal forces, the planet's core lost its momentum, killing off the magnetic field.

What remain are patches of strong magnetic imprints in the oldest parts of Mars' crust. Because the fresher surface features are magnetic-free, scientists believe Mars lost its shield about four billion years ago.

Laboratory tests and computer simulations by Arkani-Hamed and colleagues and published in the Journal of Geophysical Research last month show a large asteroid circling about 46,000 miles above Mars could have had a strong enough pull on Mars to coax its liquid core into moving. The dynamic would have lasted about 400 million years before the asteroid crashed, demagnetizing Mars.

"Once it impacted, there were no tidal forces anymore so it couldn't power the dynamo," Arkani-Hamed told Discovery News.

The theory could explain why Mars' vigorous core suddenly grew still.

"Maybe a core dynamo wasn't powered by convection, but by asteroid tidal forces," he said.

Walter Kiefer with the Lunar & Planetary Institute in Houston follows the logic, but doesn't see how an asteroid as large as the one needed to tug Mars' core would have been captured by the planet's gravity in the first place.

"I just don't know how to dissipate the energy to get it into orbit around Mars, " he said. "Until that step is made, it's hard for me to regard this as the right model."

The loss of Mars' magnetic field may have played a critical role in the planet's evolution from the warm and wet world scientists suspect it was into the cold, dry desert that exists today.

Magnetic fields, similar to Earth's, protect planets from cosmic rays. They also help maintain the atmosphere by shielding molecules from solar radiation.

Siberia forest blast captivates Wollongong scientist

Brett Cox
Illawarra Mercury News
Fri, 25 Jul 2008 10:39 EDT

It's a question that has had scientists arguing for 100 years.

Now, after many came together for conferences a century after the "Tunguska Event" in a Siberian Forest, the arguments continue.

On June 30, 1908, a blast, hundreds of times more powerful than the Hiroshima atomic bomb, destroyed about 2000sq km of forest but left no obvious crater.

Wollongong academic Ted Bryant at the Tunguska site.

Ted Bryant, Associate Dean of the Science Faculty at the University of Wollongong, was one of a number of scientists from around the world to converge on the area in recent weeks. He took part in one of four conferences where scientists gave presentations.

There are 28 theories as to how the forest damage was caused, ranging from a giant UFO to an underground volcano detonated by a physicist harnessing electric charges in New York.

Professor Bryant is part of the largest group, who believe that a meteor exploded over the forest.

He stayed in Krasnoyarsk with colleagues from the Holocene Impact Working Group, a collective of scientists who believe meteorite impacts on Earth are more common than previously thought.

His group has discovered 15 possible ocean impact craters around the globe, many in shallow water, leading them to believe there are probably many more in deeper waters. The group also studies what it believes are land tsunami deposits from the impacts.

Prof Bryant says there is much passion in Russia, particularly, as scientists argue their cases over the Tunguska Event.

"There was funding from a billionaire worth about $140,000 for research arguing it was caused by a spacecraft," he said.

Prof Bryant travelled 30km into the impact zone by helicopter, camping in cabins built by the first scientists to venture there in 1928.

"Had it occurred over a city like Sydney, it would have destroyed the city," he said. "The picture with me in it shows the overturned roots of one of the trees blown down over 100 years ago.

"The (first scientists) found all the trees at this site were dead and standing up, because they were at the centre of the blast - very much like the building left standing beneath the epicentre of the Hiroshima atomic bomb blast.

"Trees were burnt on one side by radiation from the direction the meteorite entered the atmosphere. The following shock wave immediately extinguished any flames, leaving partially burnt trunks."

Some Russian scientists argue against a meteorite theory as there are no fragments and no crater.

And some scientists have been seeking what could be a small crater and deposits that did not break up in the atmosphere.

Hit or Miss? Asteroid Apophis heading our way

Russia Today
Fri, 25 Jul 2008 16:46 EDT

©Unknown

Astronomers are battling to work out the trajectory of an asteroid that will cause havoc if it hits the Earth in 2036. Called Apophis, the giant meteor is hurtling through space at 10km per second. Scientists are warning that an impact would be far more devastating than the atomic bomb dropped on Hiroshima at the end of WW2.

At the Zvenigorod Observatory near Moscow, space researchers keep watch on cosmic bodies and study known meteorites to understand their size and inner structure. They are tracking the path of the asteroid Apophis as well. They aim to determine how real the danger is but that will only be clear in a decade's time.

Astronomer Sergey Barabanov explains the predicted course of events: "The critical moment will be in 2029, when Apophis passes so close to Earth that it will be visible to the naked eye. The consequence of this fly-by will tell us whether it will come back again and collide with us in 2036," he said.

If Apophis passes through a particular point in space called a keyhole the Earth's gravity may change its course for the worst.

In ancient Egypt, Apophis was the spirit of evil and destruction, a snakelike demon determined to plunge the world into eternal darkness. A fitting name, then, for a menace that could potentially cause devastating global damage.

Nasa estimates the blast caused by Apophis would be a 100,000 times more powerful than the bomb dropped on Hiroshima at the end of WW2.

It would also be more destructive than Siberia's Tunguska event of 100 years ago. That is thought to have been caused by a small space rock explosion and this impact is the largest in Earth's recent history. It wreaked havoc on a vast area, wiping out 80 million trees.

Ideas on how to deflect an asteroid range from blowing it up to sending a spacecraft to nudge it off its path.

Anatoly Zaitsev from the Moscow-based Planetary Defence Centre says we need to develop "a planetary protection system."

"There's no point in discovering these objects if we don't protect ourselves from them. But we also need better observation techniques. As it's difficult to track objects from the ground, I think a space observation platform would be the best option," Zaitsev said.

Meanwhile, Russia has offered to launch a space probe to plant a radio transmitter on Apophis so its orbit can be more accurately tracked.

Ex-Astronaut Slams Asteroid Plan

Sky News
Mon, 28 Jul 2008 09:05 EDT

©Sky News

A former Nasa astronaut claims plans to blast Earth-bound asteroids out of space with nuclear weapons is not the best way to beat the threat.

Apollo 9 legend Rusty Schweickart, who clocked up more than 240 hours in space, was responding to a Nasa report which said nukes were the best option to avert a catastrophic asteroid collision with Earth.

He says most heavenly bodies could be redirected by ramming them from behind or towing them to safety with unmanned spacecraft.

Speaking at a public meeting in San Francisco, Mr Schweickart says Nasa was put under political pressure to come up with the nuclear missile solution.

The astronaut-turned-scientist, who piloted the lunar capsule in Apollo 9, now heads the B612 Foundation, which promotes plans to alter the course of asteroids hurtling towards Earth.

He says that at present we simply do not know what is heading towards us, but as new powerful telescopes come online, we will have a clearer picture.

"The good news is that we can do something about this," he said.

"The marriage of we human beings and the machines that we've created are now at a level of capability which enables us to ... stop this process from occurring."

In May 2005, he told the US Congress that a mission to attach a device such as a radio transmitter to asteroid 99942 Apophis should be a high priority.

It is estimated that this asteroid has a 1 in 6,000 probability of striking the Earth in the 21st Century.

The latest data indicates that the chance of Apophis impacting the Earth is 1 in 45,000 in 2036.

Comment: The notion that "we can do something about this" may be an indulgence in more than a little wishful thinking.

Fireballs and Meteorites - SOTT.NET

02 July 2008

July 2008

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