MACROSCOPE
Better Collision Insurance
Asteroids smaller than those now being actively catalogued constitute a largely neglected natural hazard
Russell Schweickart, Clark Chapman
In October 2001, we and 22 like-minded engineers and astronomers,
including a few former and current astronauts, got together at the
Johnson Space Center in Houston to discuss what we saw as a missing
element in the space program: attention to the possibility of our
planet being struck by a near-Earth asteroid. We knew of the
accelerating rate at which such objects were being discovered. But
no one, certainly no federal or international agency, was taking
seriously the question of what exactly to do when an asteroid is
found with our address on it. During that initial meeting, less than
six weeks after the 9/11 terrorist strike, we decided that this
threat from outer space needed to be dealt with seriously and that
our group might just be able to move the process along. To
facilitate our work, we formed the B612 Foundation, a non-profit
corporation named after the home asteroid of the title character in
Antoine de Saint-Exupéry's The Little Prince.
NASA has been spending about $4 million a year to meet a 1998
Congressional mandate to chart (by 2008) at least 90 percent of the
near-Earth asteroids that are more than 1 kilometer in diameter.
NASA's Jet Propulsion Laboratory has been overseeing the effort,
called the Spaceguard Survey, which has to date discovered more than
790 of an estimated 1,100 or so of these huge, rocky objects. The
impact of a 1-kilometer asteroid would release the same amount of
energy as 70,000 megatons of TNT or, equivalently, as 1,400 of the
largest thermonuclear weapons ever detonated. The subsequent
Sun-dimming pall of debris lofted high into the atmosphere would
envelop our planet for months, threatening all of human civilization.
The need to be on the lookout for such an immense catastrophe is
clear enough, as more than one Hollywood blockbuster has made widely
known. The capability of the current search effort, however, is
inadequate to address the danger posed by the far more populous
cohort of smaller near-Earth asteroids, those down to about 100
meters in diameter. Such objects can cause serious local or even
regional destruction. The impact of a 100-meter-diameter body would
release the equivalent of an 80-megaton bomb and thus could
devastate an area the size of a large city, for example. And a
several-hundred-meter body could cause a tsunami rivaling or
exceeding last year's horrific Indian Ocean event.
Objects in this range of diameters are discovered only incidentally
today by the modest equipment that has been dedicated to finding
their larger siblings. A recent addition to the list of small
asteroids that have a small but real chance of striking the Earth is
a 330-meter-diameter asteroid named 99942 Apophis (formerly known as
2004 MN4). It has a 1-in-32,000 chance of impacting in April
2035 and a 1-in-12,000 chance of striking in April 2036. So there's
no need to become alarmed at this stage. Yet one of these smaller
asteroids is far more likely than their larger counterparts to
constitute a danger in the foreseeable future. They are also easier
to deflect away from Earth using space technology. The problem is
that today astronomers have discovered such a low percentage of the
smaller near-Earth asteroids that a strike with no warning
whatsoever is far and away more likely than our having enough time
to undertake an effort at deflection.
Hazard a Guess
In 2003, a NASA study team published a report that recommended
deploying telescopes that could bring the detection threshold of
near-Earth asteroids down to about 140 meters. Others believe that
targeting 100 meters is a more appropriate goal. Below that size,
the atmosphere largely protects us, although the best estimates of
the object that caused the 1908 Tunguska explosion (which destroyed
2,000 square kilometers of Siberian forest) was about 65 meters.
Unfortunately, no action has been taken to implement the
recommendations made in that excellent report.
Whereas scientists in the United States have done most of the
discovery work, many amateur and professional astronomers around the
world make essential follow-up observations, which allow the orbits
of the newly discovered asteroids to be refined and the
probabilities of impact to be ascertained. Specialists at both the
Jet Propulsion Laboratory (who operate the Sentry System) and the
University of Pisa (who maintain the Near-Earth Objects Dynamic
Site) do a fine job of making such information publicly available.
But only the United Kingdom has begun to address the relevant policy
issues. Unfortunately, precious little was done with the excellent
recommendations contained in the report on the topic that Parliament
mandated in January 2000. No government or international body
assigned any agency responsibility for protecting life and property
from this extraordinary kind of natural disaster.
The B612 Foundation has thus wrestled with this aspect of the
problem virtually alone. In doing so, we have discovered that when
you start paying attention to the details, both the engineering and
the policy issues are far more complex than you might assume.
First, consider the technology-development front. It happens that
NASA was, at least until recently, headed in just the right
direction for building hardware that could deflect an object away
from a collision with Earth. Prometheus is a NASA program to develop
cost-effective deep-space propulsion capability by utilizing
high-performance ion or plasma engines powered by a small nuclear
reactor—just what would be needed to give a menacing asteroid
the necessary shove. The nuclear-electric propulsion portion of the
program now seems to be on hold with priority shifted toward
developing a small reactor for future work on the lunar surface.
Just prior to the arrival of Michael Griffin as the new NASA
Administrator, an asteroid-deflection mission was in the final
throes of consideration as the first operational test of the
Prometheus technology. This mission would have demonstrated the use
of an "asteroid tugboat" to deflect near-Earth asteroids,
a concept that we and two other members of our group spelled out in
Scientific American in November 2003. However, this
proposal, along with the Prometheus program, was put into limbo in a
reshuffling of NASA priorities.
Political Moves
On the policy side, it became obvious to us that asteroid deflection
raises a host of critical issues, many of them international in
scope. Intentional deflection of an asteroid bound to hit a specific
location on Earth transforms an "act of God" (in legal
parlance) into an intentional act of humankind. During deflection,
the point of impact is shifted from its original location along a
"path of risk" to a point where the asteroid barely grazes
the Earth's atmosphere. In the process, populations and property not
initially threatened are placed in jeopardy. If, for example, the
propulsion system were to fail before deflection was fully achieved,
the asteroid would then be headed for a new ground-zero, which
might, say, fall on the other side of an international border.
Shifting the point of impact might also reshape the potential and
nature of a subsequent tsunami, redistributing the risk from what it
had been before. Who then is liable? These concerns are just the tip
of one large and messy policy iceberg, but they exemplify very
significant matters with which no nation on Earth is currently dealing.
The B612 Foundation recently called this absence of government
involvement to the attention of the U.S. Congress. We suggested that
responsibility for protecting the Earth from impact hazards be
analyzed and assigned to some agency of the U.S. government. Most
people who are aware of the danger probably think that NASA already
has this duty, but in fact it doesn't. The scientists of NASA have
done an excellent job in discovering and cataloging these objects,
but their work, and to a large extent their thinking, has stopped
there. But thanks in large part to Texas Congressman John Culberson,
who has taken a strong interest in this issue, this vacuum is about
to be filled. As of this past June, NASA has been instructed to
assess what actions would be necessary to protect our planet from
asteroid impacts.
This recent Congressional action is a welcome development. We hope
that NASA will take its new charge seriously and examine the many
elements involved in full depth. Now might be an excellent time for
NASA to request that the National Academy of Sciences (which has
been silent on the issue) weigh in and recommend the proper steps to
take to integrate the management of this threat into the wider array
of responses to natural and human-caused hazards to society.
Although the task of providing an early warning has gotten off to a
good start, it is just a start. It's fine to know about the
possibility of infrequent civilization-busters, but it is well past
time to look systematically for the much more numerous 100- to
200-meter objects. Furthermore, once astronomers have reported their
data and made their calculations for the likelihood of an impact,
other professionals need to assess the hazard and inform the
public—both about the potential for damage and about the
practical options available to eliminate, or at least mitigate, the risk.
In addition, we believe that it is critical that the technologies
necessary to deflect a near-Earth asteroid be developed beyond the
current sketchy plans and that an actual demonstration be executed
within the next decade or so. After all, you always learn best by doing.
Perhaps most challenging, but vitally important, is to bring
together the institutional players, both domestic and international,
who must ultimately make the difficult choices about when and under
what circumstances we should attempt to deflect a threatening
asteroid—and what risks and costs we are willing to accept in
the process. Right now no one has any inkling about how these
decisions would be made.
Although the frequency of asteroid impacts is very low compared with
most other natural hazards, none has the same enormous potential for
devastation. Conversely, a catastrophic collision with an asteroid,
unlike any other major natural disaster, can be avoided
entirely—provided that we do our homework in time and with diligence.
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