Computer Science
Scientific paper
May 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997nyasa.822..283m&link_type=abstract
Near-Earth Objects, the United Nations International Conference: Proceedings of the international conference held April 24-26, 1
Computer Science
Asteroids, Meteorites, Meteoroids, Terminal Ballistics, Atmospheric Effects, Atmospheric Composition, Projectiles, Lower Atmosphere, Wakes, Venus Atmosphere, Venus (Planet), Size Distribution, Iron, Ambience
Scientific paper
Small comets and asteroids that strike a planet possessing an atmosphere do not invariably strike the surface. The atmosphere resists penetration by high velocity projectiles in two ways. First, the projectile must push aside the atmospheric gases to reach the surface. This requires that the mass of gas swept aside by the projectile is roughly comparable to its own mass. For a stony object striking the Earth, this means that rigid meteoroids up to a few meters in diameter will be stopped in the atmosphere. The second important effect of the atmosphere is to crush fast-incoming meteoroids. The pressure in front of a projectile traveling with velocity nu is rho nu2, where p is the density of the ambient atmosphere. The pressure in the wake behind it is near zero. This differential pressure tends to crush the meteoroid and disperse its fragments. Stresses on typical incoming objects may reach tens of kilobars in the lower atmosphere, large enough to shatter all but the strongest iron meteoroids. When an object is crushed, its fragments experience much more drag than they would experience as an intact body, and thus have more difficulty reaching the surface. Stony objects less than about a hundred meters in diameter do not reach the surface, instead depositing their energy in an airburst similar to that of the 1908 Tunguska, Siberia explosion. This process is well documented by crater size distributions and strewn fields produced by fragmented meteorites on both the Earth and on Venus, although the 100 times thicker atmosphere of Venus is proportionately more effective in screening approaching asteroids and comets. The size of the impact-generated strewn fields is typically a kilometer or two on Earth, but averages about 20 km on Venus.
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