Introduction

    FOR 24 HOURS earlier this month, the biggest story on the planet was the threat that it might be struck by a mile-wide asteroid. On March 11 the Smithsonian Astrophysical Observatory in Cambridge, Mass., announced that on Oct. 26, 2028, at 1:30 p.m. EST, Asteroid 1997 XF11 would likely pass within 30,000 miles of the Earth and might even hit. Astronomers worldwide were asked to obtain additional data to plot the asteroid's course more precisely.

    Within a day, previous approaches of the asteroid were found in archived photographs, and the path was recalculated. The Jet Propulsion Laboratory in Pasadena, Calif., announced that the object would pass 600,000 miles away--well outside the moon's orbit of 240,000 miles. [FN1] What had loomed as a threat of global cataclysm became fodder for Jay Leno and a classic New York Post headline, "Kiss Your Asteroid Goodbye." As it happens, just a year ago, at a New York University Environmental Law Journal symposium on the law of outer space exploration and development, this writer and colleague Anna Barber presented a paper on legal issues in defending against asteroids and comets. [FN2] There actually are substantial legal issues, chiefly relating to the principal method that would be used to defend against an incoming object: the launch of nuclear weapons. Both U.S. and international law regulate the use of such weapons in space.

    This column begins by outlining the nature of the threat and the proposals to defend against it. It then compares the risk of a comet or asteroid impact to other risks with which society concerns itself. It will then turn to how domestic law, especially the National Environmental Policy Act, affects a system to defend against this threat and, then, how defensive measures are affected by international law, especially the Outer Space Treaty and the nuclear non-proliferation agreements.

The Threat

    The Earth's orbit crosses the orbits of swarms of comets and asteroids. Astronomers have catalogued more than 180 asteroids and 26 comets in orbits that intersect the Earth's. The largest are comparable to the one that killed off the dinosaurs 65 million years ago. Only a small fraction of Earth-crossing objects have been found so far; it is believed there are roughly 2,000 such objects of at least 1 kilometer in size. [FN3]

    Now that the risk of 1997 XF11 has been discounted, none of the known objects is expected to collide with the Earth for at least the next two centuries. We cannot predict about the 1,800 or so unknown but expected near-Earth objects until they are found and their orbits are calculated. (1997 XF11 itself was only discovered on Dec. 6, 1997.) Even less is known about long-period comets that quickly approach the inner planets from beyond the solar system.

    Overall, current estimates are that objects about 10 meters across strike the Earth almost annually, with an explosive force of about 10,000 tons of TNT (roughly the yield of the Hiroshima bomb), but break up harmlessly (although noisily) in the atmosphere; objects about 100 meters across, such as the one that destroyed hundreds of square miles in the Tunguska region of Siberia in 1908, arrive about once every 300 years; one about four times the size of Tunguska's, expected every few thousand years, could, if it landed in an ocean, cause tsunamis with waves more than 60 meters high that would wipe out coastal cities in all directions.

    Objects about one kilometer across hit once in 500,000 years and can cause catastrophic global effects and the death of billions. 1997 XF11 is thought to be about twice that size; it would have been indescribably bad luck for such an object to hit during our time (although, jarring as it is to say, better now than before the advent of nuclear weapons).

    Relatively little is being done to detect these expected 1,800 Earth-crossing objects. Only a handful of astronomers are at work full-time in this effort. The few observatories engaged in this search periodically have to lay off their staffs when they run out of money, and they must send out fundraising appeals to the public and accept donations from bake sales. Since a program in Australia was closed in 1996 for budgetary reasons, there have been no systematic observations at all from the Southern Hemisphere--although much of the sky can only be seen from there.

    The total worldwide cost of an adequate asteroid/comet search program has been estimated at about $50 million in capital cost (mostly for new telescopes) and $10 million in annual operating costs. In the scheme of defense spending, and even environmental spending, those are tiny numbers, but the money has not been made available.

Defensive Measures

    If a near-Earth object (NEO) is found to be on a collision course with the Earth, the natural first reaction is to attempt to blow it up. However, this could be counterproductive if several of the resulting fragments are still heading toward us and large enough to penetrate our atmosphere; that could increase rather than decrease the destruction upon arrival. It is better to deflect an object than to fragment it if there is enough warning time. The idea is simply to move the asteroid or comet enough so that it and the Earth will not be at the same place at the same time.

    Nuclear devices seem to be the only currently available technology that can deliver enough energy to move a large object far enough to avoid an Earth impact. For smaller NEOs, non-nuclear options may be available.

    Deflection requires abundant advance warning. Fortunately, Earth-crossing asteroids that are large enough to pose a global threat are likely to be discovered decades, if not centuries or millennia, in advance of collision, so there would be ample time to decide on a strategy, develop the technology and carry out the mission. Had 1997 XF11 been found to be on a collision course, the 30 years until impact should have been adequate.

    A qualitatively different problem is posed by long-period comets, which have periods of revolution around the Sun exceeding 200 years; some have orbital periods of millions of years. Thus any long-period comet that comes into view is likely being seen by humanity for the first time. They move much faster than asteroids and their trajectories are difficult to predict precisely because their paths are influenced not only by gravity, but also by the solar forces that also generate their tails.

    Such comets are likely to be spotted 250 to 500 days before impact, but it can be shorter; if the comet comes from a direction behind the sun, we might have only a few days' or hours' notice. That leaves no time for deflection and very little for deliberation and preparation; the only hope of defense would be to have nuclear-armed spacecraft ready for launch, or in standby orbits.

    Fortunately, long-period comets represent only a tiny fraction of the objects that may hit the Earth, so the odds that one will strike here in the next several centuries are microscopic.

Comparative Risks

    Now that we have discussed the nature of the risk, we will compare it to other more familiar, and more guarded-against, risks.

    One astronomer has calculated roughly that four times every million years, a large NEO will arrive that can kill 1 billion people. [FN4] The death of 4 billion people over 1 million years works out to an average of 4,000 people per year. If there are 4 billion people on the planet, an average death rate of 4,000 per year means that every year, statistically every person has a one in 1 million chance of being killed by a comet or asteroid. Of course, in actuality the results would be very lumpy, and not at all spread out as the averages suggest, but the averages do allow comparisons to more familiar risks.

    Annual deaths of 4,000 are similar to the number of people who die annually in the United States of drowning or fires, and more than those who die from ingestion of food or objects or from accidental discharge of firearms. In an average year, about 700 people worldwide die in the crashes of commercial airlines. All of these are causes of death that our society goes to great expense to try to prevent.

    An individual's statistical risk of death also receives considerable regulatory attention. For example, the U.S. Environmental Protection Agency's regulations under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, the Superfund law) declare that a one in 1 million chance of contracting cancer is the threshold for determining cleanup levels for sites contaminated with hazardous substances. [FN5] That is a lifetime risk that any person will contract a case of cancer, whether exposure to the chemicals is actual or hypothetical, without respect to the number of people actually exposed, and without respect to whether the cancers are fatal.

    Thus, on a purely statistical basis, CERCLA addresses risks that are significantly lower than those posed by comets and asteroids. CERCLA risks are addressed by remedial programs that cost on average $30 million per site. Thus the cost of cleaning up two to four average Superfund sites (there are a total of about 1,200 nationwide) is roughly the equivalent of carrying out a full-blown comet/asteroid detection program.

    If 4,000 lives a year are truly at stake in a program to guard against NEOs, one would ordinarily expect very large public expenditures to follow. The figures vary widely depending on the program involved, but a rule of thumb in assessing the costs and benefits of life-saving programs is that one life is valued at $4-8 million. At that rate, comet and asteroid detection would warrant $16 billion-32 billion per year. That exceeds what the astronomy establishment is seeking by a factor of more than a thousand.

Budget Discrepancies

    There are several possible explanations for this discrepancy:

• the statistical uncertainties involved (although the uncertainties in CERCLA risk assessments are not much lower);
• the fact that we tend psychologically to discount lives in future generations;
• and most important, the risk has an air of unreality about it, since no one is known ever to have been killed by a meteor.

    In fact, the biggest threat that asteroids pose to mankind today is probably the excuse they can provide for continuing to deploy nuclear weapons. In 1996 there were two stark examples of this. In April, China refused to sign a treaty with Russia banning nuclear weapons testing, on the stated ground that such weapons might be needed to combat the asteroid threat. In September, a "Space Protection of Earth" conference was held at the Russian Federal Nuclear Center to consider building a system of nuclear-armed missiles that could be readied for launch in 90 minutes if an incoming comet were spotted.

    It seems obvious that the deployment of a nuclear weapons system in China or Russia (or anywhere else) poses a threat of accidental or malevolent mass destruction that dwarfs the odds that such a system will be suddenly needed to beat back a long-period comet or other atypical threat that arises with too little warning to let us develop a defensive system from scratch.

    Some U.S. scientists today advocate a testing program for nuclear explosions at remote asteroids to determine the parameters under which defensive measures would best work. The development, fabrication and launch of a device to carry out such an experiment is fraught with risk. A release of dangerous quantities of radioactive material (whether or not through detonation) could occur through manufacturing error, launch failure, terrorist action or several other plausible scenarios. The probabilities of a radioactive release with locally adverse effects, or even of a catastrophic detonation, greatly exceed the chances of a long-period comet sneaking up on us.

U.S. Legal Issues

    We now turn to the legal implications of all of this, starting with the implications under U.S. law.

    Any U.S.-sponsored NEO program must comply with the requirements of U.S. environmental laws, principally the National Environmental Policy Act (NEPA). [FN6] Each of the potential NEO program activities -- land-based detection, space-based detection, interception, destruction and deflection--may have environmental impacts that must be considered.

    To document its consideration of environmental impacts, each federal agency must prepare an Environmental Impact Statement (EIS) for "every recommendation or report on proposals for legislation and other major Federal actions significantly affecting the quality of the human environment."

    A NASA-sponsored program for NEO detection and study that employs existing detection equipment and technology is unlikely to require the preparation of a full EIS. In 1996 NASA performed an environmental study, but no EIS, for its near-Earth asteroid rendezvous (NEAR) mission, scheduled to reach the asteroid 433 Eros in 1999.

    Even a simple detection program might require an EIS if it involved the construction of new telescopes on new sites or a substantial increase in the number of space launches. For example, the proposed siting of a telescope project in Arizona pitted the defenders of the endangered red squirrel against an international consortium seeking to construct several telescopes on various peaks of Mount Graham. Aided by federal legislative intervention, the telescopes were eventually approved in areas found less vital to the squirrels' survival. [FN7]

    The risk of accidental release of toxic substances--possibly including radioactive materials--has also been considered in evaluating space launches under NEPA. In two cases titled Florida Coalition for Peace and Justice v. Bush, [FN8] the plaintiffs challenged NASA's decision to go forward with particular space exploration projects. The plaintiffs' claims in both cases were brought on the ground that the EIS did not adequately assess the project's risks, especially the possibility of an accident causing the release of plutonium.

    In recent years approximately one in 10 unmanned satellite launches has failed. Several nuclear-powered space probes have either blown up, releasing plutonium into the atmosphere, or fallen back into the ocean. [FN9] The courts concluded in both cases that NASA had adequately assessed the risks of the project, and dismissed the lawsuits. A similar challenge in late 1997 failed to halt the launch of the nuclear-powered Cassini Mission to Saturn. [FN10]

    Any launches in connection with asteroid/comet defense will be dwarfed in number (and hence in environmental impact) by launches for commercial purposes. Given the greatly expanding use of satellites for telecommunications, it has been estimated that 1,700 commercial satellites will be launched in the next decade (compared to the 150 now in orbit).

    A planetary defense program -- a concerted plan for detection and for the design and testing of a NEO response system -- might trigger the preparation of a "programmatic EIS" for the development of new technology. The Star Wars program has been the subject of several programmatic EISs and numerous environmental assessments related to particular aspects of the program. Exemption from NEPA is available if the government had to quickly respond to an emergency. [FN11] This is most likely to apply to long-period comets; as discussed earlier, asteroids and short-period comets are generally slower and more predictable and can, therefore, be detected earlier. However, in the day that the 1997 XF11 seemed to be threatening, the suggestion of an EIS for the defensive measures might have been poorly received, even though possible impact was 30 years away.

International Law

    Now we turn to the implications of international law for a planetary defense program.

    The basic principles governing international activities in outer space are established by the 1967 Outer Space Treaty. [FN12] It provides that, like the high seas and the Antarctic, outer space is not subject to the sovereign jurisdiction of any nation, but rather may be exploited by all nations. Article IV of the Treaty provides that countries will not place nuclear weapons into orbit around the Earth, or station them in outer space in any other manner. Article IV also provides that no state party may test any type of weapon on any celestial body. This categorical ban would prohibit any signatory from testing any sort of NEO destruction system, even on the smallest, most remote asteroid. Any testing of a nuclear planetary defense system might also violate the multilateral 1963 Partial Test Ban Treaty, [FN13] which prohibits nuclear- weapon test explosions and any other type of nuclear explosion anywhere that is under the "jurisdiction or control" of the party conducting the explosion.

    The phrase "under its jurisdiction or control" was intended to extend the ban to non-self-governing territories, but not to territories under hostile control. In other words, the Treaty is not intended to prevent explosions in enemy territory during armed hostilities. Arguments could be made either way about whether this Treaty would apply to testing nuclear weapons on asteroids. Neither the Partial Test Ban Treaty nor the Outer Space Treaty prohibits the launch of ballistic missiles carrying nuclear weapons and headed toward an enemy. The Outer Space Treaty does provide that parties shall "conduct exploration of [celestial bodies] so as to avoid their harmful contamination." This provision arguably bans blowing up asteroids or comets, altering their orbits or contaminating them with large amounts of radiation.

    There is a compelling argument that no international obligation would prevent the launching of a missile with the aim of diverting or destroying a threatening NEO. The launching country should be able to invoke the justification of self- defense, the right to which is codified in the UN Charter. Complexities can arise, however, if scientists disagree over the best tactics to use. A nuclear device could divert a threatening object, but (depending on the composition--some NEOs are mostly rock, some iron and some ice, and all would behave differently in a blast) perhaps an explosion could also fragment it, causing much more harm than good. The 1972 Convention on International Liability for Damage Caused by Space Objects [FN14] provides that a launching state is strictly liable for damage caused on the surface of the Earth or to aircraft in flight caused by objects launched into space. For other types of damage, the launching party is only liable if it is at fault. Debris from exploded comets or asteroids entering the Earth's atmosphere, or failed launches of anti-asteroid weapons, could cause much greater damage than satellites falling back to Earth. Under the Liability Convention, nations might be responsible for any damage caused in other parts of the world as a result of either the testing or the deployment of a planetary defense system.

Conclusion

    If international concern regarding NEOs increases, a treaty addressing the subject might be in order. Such a treaty might call for:

• full transparency of national NEO response efforts;
• exculpation of nations launching spacecraft as agreed and authorized by the international NEO program;
• establishment of an NEO detection and response agency to manage the international effort, perhaps through the United Nations;
• formalization of information-and technology-sharing processes; institution of emergency response procedures to address both potential NEO collisions and accidents; and
• prohibition of any unilateral planetary defense program except in the case of emergencies.

    The immediate priority for the international community should be to increase the rate of asteroid and comet detection. The very first step might be to reopen the Australian observation program and thereby allow again the tracking of objects that can be seen only from the Southern Hemisphere. This would cost an almost comically low $250,000 a year or so. Perhaps some reader of this column can find a donor who can provide this sum.

FN1. Central Bureau of Astronomical Telegrams, International Astronomical Union, "Circular No. 6839: 1997 XF11,"  previously available on the Harvard University server.  If you find it elsewhere, please notify the author.
FN2. This paper has been published as Michael B. Gerrard and Anna W. Barber, "Asteroids and Comets: U.S. and International Law and the Lowest-Probability, Highest-Consequence Risk," 6 N.Y.U. Env'l L.J. 4 (1997). It contains considerably more detail and many more legal citations than this column.
FN3. See generally Tom Gehrels, ed., "Hazards Due to Comets and Asteroids (1994); John L. Remo, ed., Near-Earth Objects: The United Nations International Conference (New York Academy of Sciences, 1997).
FN4. John S. Lewis, Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment 220-21 (1996). Similarly, Clark R. Chapman & David Morrison, "Impacts on the Earth by Asteroids and Comets: Assessing the Hazard," 367 Nature 33 (1994).
FN5. 40 CFR Sec. 300.430(e)(2)(A)(2).
FN6. 42 USC Secs. 4321-4347.
FN7. Mount Graham Coalition v. Thomas, 89 F3d 554 (9th Cir. 1996).
FN8. 1990 U.S. Dist. Lexis 13345 (D.C. Cir. Oct. 5, 1990); 1989 U.S. Dist. Lexis 12003 (D.C. Cir. Oct. 10, 1989).
FN9. See, generally, Karl Grossman, The Wrong Stuff: The Space Program's Nuclear Threat to Our Planet (1997).
FN10. Hawaii County Green Party v. Clinton, 980 F. Supp. 1160 (D. Ha.1997), motion for reconsideration denied, 1997 U.S. Dist. Lexis 16301 (D. Ha. 1997).
FN11. 40 CFR Sec. 1506.11.
FN12. "Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies," opened for signature Jan. 27, 1967, 18 UST 2410, 610 UNTS 205 (entered
into force Oct. 10, 1967).
FN13. "Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water," Aug. 5, 1963, 480 UNTS 43. FN14. 24 UST 2389.

Michael B. Gerrard has practiced environmental law in New York City since 1978, and is a partner in the law firm of Arnold & Porter, and a member of the adjunct faculties of Columbia Law School and the Yale School of Forestry and Environmental Studies.  He is author or editor of four books on environmental law, most recently Brownfields Law & Practice: The Cleanup and Redevelopment of Contaminated Land (Matthew Bender & Co., two volumes, 1998). E-mail: Michael_Gerrard@aporter.com.

Michael B. Gerrard's paper is published online with his permission by Ray Martin  as a service to the Risk Analysis Discussion Group with a subscription page at http://www.sra.org/riskanal.htm .   Ray Martin's home page menu is at: 

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