John Remo has organized a United Nations Conference on "Near-Earth Objects: Interactions With Asteroids and Comets." On 16 January 1998 he spoke on the same subject to the Physics and Astronomy Section of the New York Academy of Sciences. NEOs: Asteroids and Comets
Sixty percent of all near-earth objects (NEOs, as he called them) are Earth-crossing asteroids, and the other forty percent are comets, half of them periodic (with periods from four to 200 years) and the other half long-period (from the Oort cloud).
Asteroids have a higher collision probability with the Earth (about 12,000 events per billion yeras) than do comets (about 2000 events per billion years from the Kuiper belt). Yet the comets pose a greater danger because of their higher collision velocity (60-70 km/hr), coming in from the Kuiper belt (located 50 times as far from the sun as Earth in the same plane as that of all the planetary orbits except that of Pluto) or the Oort cloud (a spherical distribution around the sun extending as far from the sun as 50,000 times the radius of Earth's orbit). Moreover, perturbation by Jupiter and by jets given off by comets make the behavior of comets far more unpredictable than that of asteroids. Yet, the orbits of all five meteorites recovered from the Erath have been charted, and have been found to be asteroids.
Remo saw no point in worrying about future collisions of NEOs with Earth but rather advocated planning through mitigation measures. Because of their unpredictability, comets give us warning times on the order of months; but the warning times for more predictable asteroids range from years to decades. During that warning time we would need to send a concentrated energy source beyond the moon to deflect the intruding object from its collision course with Earth. Many mechanisms have been advocated, including solar sails, microwaves, conventional explosives, and lasers. Remo found reservations with all of these. Much as he sympathized with those who sought a "non-nuclear solution," he saw no altrnative to a nuclear device sent out on a rocket.
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