(unfortunately timed near the full moon) on October 18th. NASA is taking
discoveries.
dirty snowball in order to see what lies just beneath the surface. The
, has taken the spacecraft past Earth several times on its way to a new cometary target, Hartley 2.
starting to warm up and become active in its approach of the Sun.
carbon-based molecule found on comets. In fact, comets are thought to
Earth 4.5 billion years ago. (You can represent that in a
emissions as well, and this was not seen. So, the comet is behaving
this very active comet in the coming days.
In addition, Earth-bound skywatchers may be treated to an extra surprise from Hartley 2.
debris of Comet Hartley 2.
Even if you don't see any fireballs, be sure to check out what promises to be stunning images from the
© Stéphane Guisard
odds that a potentially devastating space rock will hit Earth this
century may be as high as one in 10. So why isn't NASA trying harder to
prevent catastrophe?Breakthrough ideas have a way of seeming obvious in retrospect, and
about a decade ago, a Columbia University geophysicist named Dallas
Abbott had a breakthrough idea. She had been pondering the craters left
by comets and asteroids that smashed into Earth. Geologists had counted
them and concluded that space strikes are rare events and had occurred
mainly during the era of primordial mists. But, Abbott realized, this
deduction was based on the number of craters found on land - and because
70 percent of Earth's surface is water, wouldn't most space objects hit
the sea? So she began searching for underwater craters caused by
impacts rather than by other forces, such as volcanoes.
What she
has found is spine-chilling: evidence that several enormous asteroids
or comets have slammed into our planet quite recently, in geologic
terms. If Abbott is right, then you may be here today, reading this
magazine, only because by sheer chance those objects struck the ocean
rather than land. Abbott believes that a space object about 300 meters in
diameter hit the Gulf of Carpentaria, north of Australia, in 536 A.D. An
object that size, striking at up to 50,000 miles per hour, could
release as much energy as 1,000 nuclear bombs. Debris, dust, and gases
thrown into the atmosphere by the impact would have blocked sunlight,
temporarily cooling the planet - and indeed, contemporaneous accounts
describe dim skies, cold summers, and poor harvests in 536 and 537. "A
most dread portent took place," the Byzantine historian Procopius wrote
of 536; the sun "gave forth its light without brightness." Frost
reportedly covered China in the summertime. Still, the harm was
mitigated by the ocean impact. When a space object strikes land, it
kicks up more dust and debris, increasing the global-cooling effect; at
the same time, the combination of shock waves and extreme heating at the
point of impact generates nitric and nitrous acids, producing rain as
corrosive as battery acid.
If the Gulf of Carpentaria object
were to strike Miami today, most of the city would be leveled, and the
atmospheric effects could trigger crop failures around the world.What's more, the Gulf of Carpentaria object was a skipping stone
compared with an object that Abbott thinks whammed into the Indian Ocean
near Madagascar some 4,800 years ago, or about 2,800 B.C. Researchers
generally assume that a space object a kilometer or more across would
cause significant global harm: widespread destruction, severe acid rain,
and dust storms that would darken the world's skies for decades. The
object that hit the Indian Ocean was three to five kilometers across,
Abbott believes, and caused a tsunami in the Pacific 600 feet high -
many times higher than the 2004 tsunami that struck Southeast Asia.
Ancient texts such as Genesis and the Epic of Gilgamesh support her
conjecture, describing an unspeakable planetary flood in roughly the
same time period. If the Indian Ocean object were to hit the sea now,
many of the world's coastal cities could be flattened. If it were to hit
land, much of a continent would be leveled; years of winter and mass
starvation would ensue.
At the start of her research, which has sparked much debate among
specialists, Abbott reasoned that if colossal asteroids or comets strike
the sea with about the same frequency as they strike land, then given
the number of known land craters, perhaps 100 large impact craters might
lie beneath the oceans.
In less than a decade of searching, she
and a few colleagues have already found what appear to be 14 large
underwater impact sites. That they've found so many so rapidly is hardly
reassuring.Other scientists are making equally unsettling discoveries. Only in the
past few decades have astronomers begun to search the nearby skies for
objects such as asteroids and comets (for convenience, let's call them
"space rocks"). What they are finding suggests that near-Earth space
rocks are more numerous than was once thought, and that their orbits may
not be as stable as has been assumed.
There is also reason to
think that space rocks may not even need to reach Earth's surface to
cause cataclysmic damage. Our solar system appears to be a far more
dangerous place than was previously believed.The received wisdom about the origins of the solar system goes something
like this: the sun and planets formed about 4.5 billion years ago from a
swirling nebula containing huge amounts of gas and dust, as well as
relatively small amounts of metals and other dense substances released
by ancient supernova explosions. The sun is at the center; the denser
planets, including Earth, formed in the middle region, along with many
asteroids - the small rocky bodies made of material that failed to
incorporate into a planet. Farther out are the gas-giant planets, such
as Jupiter, plus vast amounts of light elements, which formed comets on
the boundary of the solar system. Early on, asteroids existed by the
millions; the planets and their satellites were bombarded by constant,
furious strikes. The heat and shock waves generated by these impacts
regularly sterilized the young Earth. Only after the rain of space
objects ceased could life begin; by then, most asteroids had already
either hit something or found stable orbits that do not lead toward
planets or moons. Asteroids still exist, but most were assumed to be in
the asteroid belt, which lies between Mars and Jupiter, far from our
blue world.
As for comets, conventional wisdom held that they also bombarded the
planets during the early eons. Comets are mostly frozen water mixed with
dirt. An ancient deluge of comets may have helped create our oceans;
lots of comets hit the moon, too, but there the light elements they were
composed of evaporated. As with asteroids, most comets were thought to
have smashed into something long ago; and, because the solar system is
largely void, researchers deemed it statistically improbable that those
remaining would cross the paths of planets.
These standard assumptions - that remaining space rocks are few, and
that encounters with planets were mainly confined to the past - are
being upended. On March 18, 2004, for instance, a 30-meter asteroid
designated 2004 FH - a hunk potentially large enough to obliterate a
city - shot past Earth, not far above the orbit occupied by
telecommunications satellites. (Enter "2004 FH" in the search box at
Wikipedia and you can watch film of that asteroid passing through the
night sky.) Looking at the broader picture, in 1992 the astronomers
David Jewitt, of the University of Hawaii, and Jane Luu, of the
Massachusetts Institute of Technology, discovered the Kuiper Belt, a
region of asteroids and comets that starts near the orbit of Neptune and
extends for immense distances outward. At least 1,000 objects big
enough to be seen from Earth have already been located there. These
objects are 100 kilometers across or larger, much bigger than whatever
dispatched the dinosaurs; space rocks this size are referred to as
"planet killers" because their impact would likely end life on Earth.
Investigation of the Kuiper Belt has just begun, but there appear to be
substantially more asteroids in this region than in the asteroid belt,
which may need a new name.
Beyond the Kuiper Belt may lie the hypothesized Oort Cloud, thought to
contain as many as trillions of comets. If the Oort Cloud does exist,
the number of extant comets is far greater than was once believed. Some
astronomers now think that short-period comets, which swing past the sun
frequently, hail from the relatively nearby Kuiper Belt, whereas comets
whose return periods are longer originate in the Oort Cloud.
But if large numbers of comets and asteroids are still around, several
billion years after the formation of the solar system, wouldn't they by
now be in stable orbits - ones that rarely intersect those of the
planets? Maybe not. During the past few decades, some astronomers have
theorized that the movement of the solar system within the Milky Way
varies the gravitational stresses to which the sun, and everything that
revolves around it, is exposed. The solar system may periodically pass
close to stars or groups of stars whose gravitational pull affects the
Oort Cloud, shaking comets and asteroids loose from their orbital
moorings and sending them downward, toward the inner planets.
Consider objects that are already near Earth, and the picture gets even
bleaker. Astronomers traditionally spent little time looking for
asteroids, regarding them as a lesser class of celestial bodies, lacking
the beauty of comets or the significance of planets and stars. Plus,
asteroids are hard to spot - they move rapidly, compared with the rest
of the heavens, and even the nearby ones are fainter than other objects
in space. Not until the 1980s did scientists begin systematically
searching for asteroids near Earth. They have been finding them in
disconcerting abundance.
In 1980, only 86 near-Earth asteroids and comets were known to exist. By
1990, the figure had risen to 170; by 2000, it was 921; as of this
writing, it is 5,388. The Jet Propulsion Laboratory, part of NASA, keeps
a running tally at www.neo.jpl.nasa.gov/stats. Ten years ago, 244
near-Earth space rocks one kilometer across or more - the size that
would cause global calamity - were known to exist; now 741 are. Of the
recently discovered nearby space objects, NASA has classified 186 as
"impact risks" (details about these rocks are
here).
And because most space-rock searches to date have been low-budget
affairs, conducted with equipment designed to look deep into the
heavens, not at nearby space, the actual number of impact risks is
undoubtedly much higher. Extrapolating from recent discoveries, NASA
estimates that there are perhaps 20,000 potentially hazardous asteroids
and comets in the general vicinity of Earth.
There's still more bad news. Earth has experienced several mass
extinctions - the dinosaurs died about 65 million years ago, and
something killed off some 96 percent of the world's marine species about
250 million years ago. Scientists have generally assumed that whatever
caused those long-ago mass extinctions - comet impacts, extreme volcanic
activity - arose from conditions that have changed and no longer pose
much threat. It's a comforting notion - but what about the mass
extinction that occurred close to our era?
About 12,000 years ago, many large animals of North America started
disappearing - woolly mammoths, saber-toothed cats, mastodons, and
others. Some scientists have speculated that Paleo-Indians may have
hunted some of the creatures to extinction. A millennia-long mini - Ice
Age also may have been a factor. But if that's the case, what explains
the disappearance of the Clovis People, the best-documented Paleo-Indian
culture, at about the same time? Their population stretched as far
south as Mexico, so the mini - Ice Age probably was not solely
responsible for their extinction.
A team of researchers led by Richard Firestone, of the Lawrence Berkeley
National Laboratory, in California, recently announced the discovery of
evidence that one or two huge space rocks, each perhaps several
kilometers across, exploded high above Canada 12,900 years ago. The
detonation, they believe, caused widespread fires and dust clouds, and
disrupted climate patterns so severely that it triggered a prolonged
period of global cooling. Mammoths and other species might have been
killed either by the impact itself or by starvation after their food
supply was disrupted. These conclusions, though hotly disputed by other
researchers, were based on extensive examinations of soil samples from
across the continent; in strata from that era, scientists found widely
distributed soot and also magnetic grains of iridium, an element that is
rare on Earth but common in space. Iridium is the meteor-hunter's
lodestar: the discovery of iridium dating back 65 million years is what
started the geologist Walter Alvarez on his path-breaking theory about
the dinosaurs' demise.
A more recent event gives further cause for concern. As buffs of the television show
The X Fileswill recall, just a century ago, in 1908, a huge explosion occurred
above Tunguska, Siberia. The cause was not a malfunctioning alien
star-cruiser but a small asteroid or comet that detonated as it
approached the ground. The blast had hundreds of times the force of the
Hiroshima bomb and devastated an area of several hundred square miles.
Had the explosion occurred above London or Paris, the city would no
longer exist. Mark Boslough, a researcher at the Sandia National
Laboratory, in New Mexico, recently concluded that the Tunguska object
was surprisingly small, perhaps only 30 meters across. Right now,
astronomers are nervously tracking 99942 Apophis, an asteroid with a
slight chance of striking Earth in April 2036. Apophis is also small by
asteroid standards, perhaps 300 meters across, but it could hit with
about 60,000 times the force of the Hiroshima bomb - enough to destroy
an area the size of France.
In other words, small asteroids may
be more dangerous than we used to think - and may do considerable damage
even if they don't reach Earth's surface. 
© NASA/NSSDC
ASTEROID 243 IDA, about 35 miles long, and its moon
recently, nearly all the thinking about the risks of space-rock strikes
has focused on counting craters. But what if most impacts don't leave
craters? This is the prospect that troubles Boslough. Exploding
in the air, the Tunguska rock did plenty of damage, but if people had
not seen the flashes, heard the detonation, and traveled to the remote
area to photograph the scorched, flattened wasteland, we'd never know
the Tunguska event had happened. Perhaps a comet or two exploding above
Canada 12,900 years ago spelled the end for saber-toothed cats and
Clovis society. But no obvious crater resulted; clues to the calamity
were subtle and hard to come by.
Comets, asteroids, and the little meteors that form pleasant shooting
stars approach Earth at great speeds - at least 25,000 miles per hour.
As they enter the atmosphere they heat up, from friction, and compress,
because they decelerate rapidly. Many space rocks explode under this
stress, especially small ones; large objects are more likely to reach
Earth's surface. The angle at which objects enter the atmosphere also
matters: an asteroid or comet approaching straight down has a better
chance of hitting the surface than one entering the atmosphere at a
shallow angle, as the latter would have to plow through more air,
heating up and compressing as it descended. The object or objects that
may have detonated above Canada 12,900 years ago would probably have
approached at a shallow angle.
If, as Boslough thinks, most asteroids and comets explode before
reaching the ground, then this is another reason to fear that the
conventional thinking seriously underestimates the frequency of
space-rock strikes - the small number of craters may be lulling us into
complacency. After all, if a space rock were hurtling toward a city,
whether it would leave a crater would not be the issue - the explosion
would be the issue.A generation ago, the standard assumption was that a dangerous object
would strike Earth perhaps once in a million years. By the mid-1990s,
researchers began to say that the threat was greater: perhaps a strike
every 300,000 years. This winter, I asked William Ailor, an asteroid
specialist at The Aerospace Corporation, a think tank for the Air Force,
what he thought the risk was. Ailor's answer: a one-in-10 chance per
century of a dangerous space-object strike.
Regardless of which estimate is correct, the likelihood of an event is, of course, no predictor. Even if space strikes are
likelyonly once every million years, that doesn't mean a million years will
pass before the next impact - the sky could suddenly darken tomorrow.
Equally important, improbable but cataclysmic dangers ought to command
attention because of their scope. A tornado is far more likely than an
asteroid strike, but humanity is sure to survive the former. The chances
that any one person will die in an airline crash are minute, but this
does not prevent us from caring about aviation safety. And as Nathan
Myhrvold, the former chief technology officer of Microsoft, put it, "The
odds of a space-object strike during your lifetime may be no more than
the odds you will die in a plane crash - but with space rocks, it's like
the entire human race is riding on the plane."
Given the scientific findings, shouldn't space rocks be one of
NASA's priorities? You'd think so, but Dallas Abbott says NASA has shown
no interest in her group's work: "The NASA people don't want to believe
me. They won't even listen."NASA supports some astronomy to search for near-Earth objects, but the
agency's efforts have been piecemeal and underfunded, backed by less
than a tenth of a percent of the NASA budget. And though altering the
course of space objects approaching Earth appears technically feasible,
NASA possesses no hardware specifically for this purpose, has nearly
nothing in development, and has resisted calls to begin work on
protection against space strikes. Instead, NASA is enthusiastically
preparing to spend hundreds of billions of taxpayers' dollars on a
manned moon base that has little apparent justification. "What is in the
best interest of the country is never even mentioned in current NASA
planning," says Russell Schweickart, one of the Apollo astronauts who
went into space in 1969, who is leading a campaign to raise awareness of
the threat posed by space rocks. "Are we going to let a space strike
kill millions of people before we get serious about this?" he asks.
In January, I attended an internal NASA conference, held at agency
headquarters, during which NASA's core goals were presented in a
PowerPoint slideshow. Nothing was said about protecting Earth from space
strikes - not even researching what sorts of spacecraft might be used
in an approaching-rock emergency. Goals that were listed included
"sustained human presence on the moon for national preeminence" and
"extend the human presence across the solar system and beyond."
Achieving national preeminence - isn't the United States pretty
well-known already? As for extending our presence, a manned mission to
Mars is at least decades away, and human travel to the outer planets is
not seriously discussed by even the most zealous advocates of space
exploration. Sending people "beyond" the solar system is inconceivable
with any technology that can reasonably be foreseen; an interstellar
spaceship traveling at the fastest speed ever achieved in space flight
would take 60,000 years to reach the next-closest star system.
After the presentation, NASA's administrator, Michael Griffin, came into
the room. I asked him why there had been no discussion of space rocks.
He said,
"We don't make up our goals. Congress has not
instructed us to provide Earth defense. I administer the policy set by
Congress and the White House, and that policy calls for a focus on
return to the moon. Congress and the White House do not ask me what I
think." I asked what NASA's priorities would be if he did set the goals.
"The same. Our priorities are correct now," he answered. "We are on the
right path. We need to go back to the moon. We don't need a
near-Earth-objects program." In a public address about a month
later, Griffin said that the moon-base plan was "the finest policy
framework for United States civil space activities that I have seen in
40 years."
Actually, Congress
has asked NASA to pay more attention to
space rocks. In 2005, Congress instructed the agency to mount a
sophisticated search of the proximate heavens for asteroids and comets,
specifically requesting that NASA locate all near-Earth objects 140
meters or larger that are less than 1.3 astronomical units from the sun -
roughly out to the orbit of Mars. Last year, NASA gave Congress its
reply: an advanced search of the sort Congress was requesting would cost
about $1 billion, and the agency had no intention of diverting funds
from existing projects, especially the moon-base initiative.
How did the moon-base idea arise? In 2003, after the shuttle Columbia
was lost, manned space operations were temporarily shut down, and the
White House spent a year studying possible new missions for NASA. George
W. Bush wanted to announce a voyage to Mars. Every Oval Office occupant
since John F. Kennedy knows how warmly history has praised him for the
success of his pledge to put men on the moon; it's only natural that
subsequent presidents would dream about securing their own place in
history by sending people to the Red Planet. But the technical barriers
and even the most optimistic cost projections for a manned mission to
Mars are prohibitive. So in 2004, Bush unveiled a compromise plan: a
permanent moon base that would be promoted as a stepping-stone for a
Mars mission at some unspecified future date. As anyone with an
aerospace engineering background well knows, stopping at the moon, as
Bush was suggesting, actually would be an impediment to Mars travel,
because huge amounts of fuel would be wasted landing on the moon and
then blasting off again. Perhaps something useful to a Mars expedition
would be learned in the course of building a moon base; but if the goal
is the Red Planet, then spending vast sums on lunar living would only
divert that money from the research and development needed for Mars
hardware. However, saying that a moon base would one day support a Mars
mission allowed Bush to create the impression that his plan would not
merely be restaging an effort that had already been completed more than
30 years before. For NASA, a decades-long project to build a moon base
would ensure a continuing flow of money to its favorite contractors and
to the congressional districts where manned-space-program centers are
located. So NASA signed on to the proposal, which Congress approved the
following year.
It is instructive, in this context, to consider the agency's rhetoric
about China. The Chinese manned space program has been improving and is
now about where the U.S. program was in the mid-1960s. Stung by
criticism that the moon-base project has no real justification - 37
years ago, President Richard Nixon cancelled the final planned Apollo
moon missions because the program was accomplishing little at great
expense; as early as 1964, the communitarian theorist Amitai Etzioni was
calling lunar obsession a "moondoggle" - NASA is selling the new plan
as a second moon race, this time against Beijing. "I'll be surprised if
the Chinese don't reach the moon before we return," Griffin said. "China
is now a strategic peer competitor to the United States in space. China
is drawing national prestige from achievements in space, and there will
be a tremendous shift in national prestige toward Beijing if the
Chinese are operating on the moon and we are not. Great nations have
always operated on the frontiers of their era. The moon is the frontier
of our era, and we must outperform the Chinese there."
Wouldn't shifting NASA's focus away from wasting money on the moon and
toward something of clear benefit for the entire world - identifying and
deflecting dangerous space objects - be a surer route to enhancing
national prestige? But NASA's institutional instinct is not to ask,
"What can we do in space that makes sense?" Rather, it is to ask, "What
can we do in space that requires lots of astronauts?" That finding and
stopping space rocks would be an expensive mission with little role for
the astronaut corps is, in all likelihood, the principal reason NASA
doesn't want to talk about the asteroid threat.
NASA's lack of interest in defending against space objects leaves a void
the Air Force seems eager to fill. The Air Force has the world's
second-largest space program, with a budget of about $11 billion - $6
billion less than NASA's. The tension between the two entities is
long-standing. Many in the Air Force believe the service could achieve
U.S. space objectives faster and more effectively than NASA. And the Air
Force simply wants flyboys in orbit: several times in the past, it has
asked Congress to fund its own space station, its own space plane, and
its own space-shuttle program. Now, with NASA all but ignoring the
space-object threat, the Air Force appears to be seizing an opportunity.
All known space rocks have been discovered using telescopes designed for
traditional "soda straw" astronomy - that is, focusing on a small patch
of sky. Now the Air Force is funding the first research installation
designed to conduct panoramic scans of the sky, a telescope complex
called Pan-STARRS, being built by the University of Hawaii. By
continuously panning the entire sky, Pan-STARRS should be able to spot
many near-Earth objects that so far have gone undetected. The telescope
also will have substantially better resolving power and sensitivity than
existing survey instruments, enabling it to find small space rocks that
have gone undetected because of their faintness.
The Pan-STARRS project has no military utility, so why is the
Air Force the sponsor? One speculation is that Pan-STARRS is the Air
Force's foot in the door for the Earth-defense mission. If the Air Force
won funding to build high-tech devices to fire at asteroids, this would
be a major milestone in its goal of an expanded space presence.But space rocks are a natural hazard, not a military threat, and an Air
Force Earth-protection initiative, however gallant, would probably
cause intense international opposition. Imagine how other governments
would react if the Pentagon announced, "Don't worry about those
explosions in space - we're protecting you."
Thus, the task of defending Earth from objects falling from the skies
seems most fitting for NASA, or perhaps for a multinational civilian
agency that might be created. Which raises the question: What could
NASA, or anyone else, actually do to provide a defense?
Russell Schweickart, the former
Apollo astronaut, runs the B612
Foundation (B612 is the asteroid home of Saint-Exupéry's Little
Prince). The foundation's goal is to get NASA officials, Congress, and
ultimately the international community to take the space-rock threat
seriously; it advocates testing a means of precise asteroid tracking,
then trying to change the course of a near-Earth object.
Current telescopes cannot track asteroids or comets accurately enough
for researchers to be sure of their courses. When 99942 Apophis was
spotted, for example, some calculations suggested it would strike Earth
in April 2029, but further study indicates it won't - instead, Apophis
should pass between Earth and the moon, during which time it may be
visible to the naked eye. The Pan-STARRS telescope complex will greatly
improve astronomers' ability to find and track space rocks, and it may
be joined by the Large Synoptic Survey Telescope, which would similarly
scan the entire sky. Earlier this year, the software billionaires Bill
Gates and Charles Simonyi pledged $30 million for work on the LSST,
which proponents hope to erect in the mountains of Chile. If it is
built, it will be the first major telescope to broadcast its data live
over the Web, allowing countless professional and amateur astronomers to
look for undiscovered asteroids.
Schweickart thinks, however, that even these instruments will
not be able to plot the courses of space rocks with absolute precision. NASA
has said that an infrared telescope launched into an orbit near Venus
could provide detailed information on the exact courses of space rocks.
Such a telescope would look outward from the inner solar system toward
Earth, detect the slight warmth of asteroids and comets against the cold
background of the cosmos, and track their movements with precision.
Congress would need to fund a near-Venus telescope, though, and NASA
would need to build it - neither of which is happening.
Another means of gathering data about a potentially threatening
near-Earth object would be to launch a space probe toward it and attach a
transponder, similar to the transponders used by civilian airliners to
report their exact locations and speed; this could give researchers
extremely precise information on the object's course. There is no doubt
that a probe can rendezvous with a space rock: in 2005, NASA smashed a
probe called Deep Impact into the nucleus of comet 9P/Tempel in order to
vaporize some of the material on the comet's surface and make a
detailed analysis of it. Schweickart estimates that a mission to attach a
transponder to an impact-risk asteroid could be staged for about $400
million - far less than the $11.7 billion cost to NASA of the 2003
Columbia disaster.
Then what? In the movies, nuclear bombs are used to destroy space rocks.
In NASA's 2007 report to Congress, the agency suggested a similar
approach. But nukes are a brute-force solution, and because an
international treaty bans nuclear warheads in space, any proposal to use
them against an asteroid would require complex diplomatic agreements.
Fortunately, it's likely that just causing a slight change in course
would avert a strike. The reason is the mechanics of orbits. Many people
think of a planet as a vacuum cleaner whose gravity sucks in everything
in its vicinity. It's true that a free-falling body will plummet toward
the nearest source of gravity - but in space, free-falling bodies are
rare. Earth does not plummet into the sun, because the angular momentum
of Earth's orbit is in equilibrium with the sun's gravity. And asteroids
and comets swirl around the sun with tremendous angular momentum, which
prevents them from falling toward most of the bodies they pass,
including Earth.
For any space object approaching a planet, there exists a "keyhole" - a
patch in space where the planet's gravity and the object's momentum
align, causing the asteroid or comet to hurtle toward the planet.
Researchers have calculated the keyholes for a few space objects and
found that they are tiny, only a few hundred meters across - pinpoints
in the immensity of the solar system. You might think of a keyhole as
the win-a-free-game opening on the 18th tee of a cheesy, incredibly
elaborate miniature-golf course. All around the opening are rotating
windmills, giants stomping their feet, dragons walking past, and other
obstacles. If your golf ball hits the opening precisely, it will roll
down a pipe for a hole in one. Miss by even a bit, and the ball caroms
away.
Tiny alterations might be enough to deflect a space rock headed toward a
keyhole. "The reason I am optimistic about stopping near-Earth-object
impacts is that it looks like we won't need to use fantastic levels of
force," Schweickart says. He envisions a "gravitational tractor," a
spacecraft weighing only a few tons - enough to have a slight
gravitational field. If an asteroid's movements were precisely
understood, placing a gravitational tractor in exactly the right place
should, ever so slowly, alter the rock's course, because low levels of
gravity from the tractor would tug at the asteroid. The rock's course
would change only by a minuscule amount, but it would miss the
hole-in-one pipe to Earth.
Will the gravitational-tractor idea work? The B612 Foundation recommends
testing the technology on an asteroid that has no chance of approaching
Earth. If the gravitational tractor should prove impractical or
ineffective, other solutions could be considered. Attaching a rocket
motor to the side of an asteroid might change its course. So might
firing a laser: as materials boiled off the asteroid, the expanding
gases would serve as a natural jet engine, pushing it in the opposite
direction.
But when it comes to killer comets, you'll just have to lose sleep over
the possibility of their approach; there are no proposals for what to do
about them. Comets are easy to see when they are near the sun and
glowing but are difficult to detect at other times. Many have
"eccentric" orbits, spending centuries at tremendous distances from the
sun, then falling toward the inner solar system, then slingshotting away
again. If you were to add comets to one of those classroom models of
the solar system, many would need to come from other floors of the
building, or from another school district, in order to be to scale.
Advanced telescopes will probably do a good job of detecting most
asteroids that pass near Earth, but an unknown comet suddenly headed our
way would be a nasty surprise. And because many comets change course
when the sun heats their sides and causes their frozen gases to expand,
deflecting or destroying them poses technical problems to which there
are no ready solutions. The logical first step, then, seems to be to
determine how to prevent an asteroid from striking Earth and hope that
some future advance, perhaps one building on the asteroid work, proves
useful against comets.
None of this will be easy, of course. Unlike in the movies, where
impossibly good-looking, wisecracking men and women grab space suits and
race to the launchpad immediately after receiving a warning that
something is approaching from space, in real life preparations to defend
against a space object would take many years. First the necessary
hardware must be built - quite possibly a range of space probes and
rockets. An asteroid that appeared to pose a serious risk would require
extensive study, and a transponder mission could take years to reach it.
International debate and consensus would be needed: the possibility of
one nation acting alone against a space threat or of, say, competing
U.S. and Chinese missions to the same object, is more than a little
worrisome. And suppose Asteroid X appeared to threaten Earth. A mission
by, say, the United States to deflect or destroy it might fail, or even
backfire, by nudging the rock toward a gravitational keyhole rather than
away from it. Asteroid X then hits Costa Rica; is the U.S. to blame? In
all likelihood, researchers will be unable to estimate where on Earth a
space rock will hit. Effectively, then, everyone would be threatened,
another reason nations would need to act cooperatively - and achieving
international cooperation could be a greater impediment than designing
the technology.
We will soon have a new president, and thus an opportunity to reassess
NASA's priorities. Whoever takes office will decide whether the nation
commits to spending hundreds of billions of dollars on a motel on the
moon, or invests in space projects of tangible benefit - space science,
environmental studies of Earth, and readying the world for protection
against a space-object strike. Although the moon-base initiative has
been NASA's focus for four years, almost nothing has yet been built for
the project, and comparatively little money has been spent; current
plans don't call for substantial funding until the space-shuttle program
ends, in 2010. This suggests that NASA could back off from the moon
base without having wasted many resources. Further, the new Ares rocket
NASA is designing for moon missions might be just the ticket for an
asteroid-deflection initiative.
Congress, too, ought to look more sensibly at space priorities. Because
it controls federal funding, Congress holds the trump cards. In 2005, it
passively approved the moon-base idea, seemingly just as budgetary
log-rolling to maintain spending in the congressional districts favored
under NASA's current budget hierarchy. The House and Senate ought to
demand that the space program have as its first priority returning
benefits to taxpayers.
It's hard to imagine how taxpayers could
benefit from a moon base. It's easy to imagine them benefiting from an
effort to protect our world from the ultimate calamity.Gregg Easterbrook is a contributing editor of The Atlantic and The
New Republic, a fellow at the Brookings Institution, and the author,
most recently, of The Progress Paradox (2003).
Comment: To see the staggering number of 'die-offs' around the world depicted on the world map (with links to the news stories) click here