Defend Earth in the Cosmic Shooting Gallery

EARTH exists in a ``shooting gallery.'' Asteroids and other primordial debris whiz past our planet's orbit yearly. It's time to take the risk of collision seriously. The American Institute of Aeronautics and Astronautics (AIAA) warns in a position paper that ``earth-orbit-crossing asteroids [called Apollo asteroids] clearly present a danger to Earth and its inhabitants.''

These missiles would hit with the energy of multi-megaton nuclear bombs. In today's highly populated world, ``the resulting disaster is likely to be without precedent,'' the AIAA says.

The institute is not being alarmist. There is nothing new about its risk assessment. What is new is our ability to do something about it. A global asteroid watch could be established at modest cost with modern telescope technology. Furthermore, the missile-destroying technologies being developed for the United States Strategic Defense Initiative (SDI) and the Soviet counterpart could be turned into an asteroid defense.

The AIAA notes that ``since 1908 there has been one direct hit [in an unpopulated area of Siberia], one atmospheric entry, and at least two near misses.'' It adds, ``In view of the fact that we have the technology needed to detect and track such an object, and possibly divert it from an impending impact, we would be derelict if we did nothing.''

Thus, the AIAA urges setting up an international detection system. It then suggests that the United States, the Soviet Union, and other interested nations explore the possibility of an asteroid shield.

For science-fiction buffs and a small group of Massachusetts Institute of Technology alumni, that should evoke a sense of deja vu. Two decades ago, the alumni (then students) took on the ambitious study project of developing a plan to protect Earth from an imagined collision with the Apollo asteroid Icarus. They worked through the technical, economic, and managerial problems of a mission to deflect or destroy the asteroid with nuclear explosions. Their Project Icarus report later became the plot for a rather good B movie involving United States-Soviet cooperation in using secret orbiting nuclear weapons to save Earth.

Now science fiction is becoming fact - at least to the extent that a number of experts seriously urge that we mount an asteroid/comet watch and consider an asteroid defense. One may be tempted merely to smile at what may seem a quixotic or eccentric suggestion. But a great deal has been learned about asteroid/comet risk in the past 20 years. Solar system scientists now recognize that the probability of a collision with Earth is not negligible.

David Morrison of the NASA-Ames Research Center and Clark R. Chapman of the Planetary Science Institute explain at length in the March issue of Sky and Telescope that recognition of the significance of what they call the ``cosmic shooting gallery'' has revolutionized scientists' views of solar-system evolution. They now know that impacts have been a major factor in shaping planets and remain a significant threat even today.

Furthermore, it now is apparent that thousands of asteroids and comets cross our orbit. One asteroid a bit larger than an aircraft carrier would have hit Earth last year with some 1,000 megatons of energy if we had passed through the collision point a mere six hours earlier.

Governments should listen to the AIAA, invest a few tens of millions of dollars in asteroid research and detection, and begin to explore the practicality of asteroid defense.

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