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Collisions of small Spacewatch asteroids with the EarthThe discovery, with the Spacewatch Telescope, of 8 Earth-approaching objects smaller than 100 m in diameter has been reported. I have calculated the probability and velocity of collision with Earth for each of these objects. Using a code we have successfully employed to model the Tunguska and Revelstoke atmospheric explosions, I have simulated the entry of these objects into Earth's atmosphere, assuming iron, stony, carbonaceous, and cometary compositions. The smallest of these objects, with tens to hundreds of kilotons of kinetic energy, pose a substantial threat at the surface only if they are iron objects. An object is taken to 'pose a substantial threat' if it either craters the ground, or explodes in the atmosphere with sufficient energy at low enough altitude to create an overpressure at the surface capable of felling trees or destroying buildings. Larger objects, with energies greater than about a megaton, devastate the surface regardless of whether they are of iron, stony, or carbonaceous composition. Iron objects crater the ground, whereas stony and carbonaceous objects explode in the atmosphere low enough to fell trees and damage buildings over thousands of square kilometers. Spacewatch objects, if presumed to be of carbonaceous composition, are as dangerous as their stony counterparts, as the former objects' lower yield strengths (and hence, higher explosion altitudes) are roughly compensated by their larger masses (as derived from their lower albedos for a given observed magnitude). Although comets are intrinsically less dangerous than asteroids, the 90 m diameter Spacewatch objects would devastate hundreds of square kilometers at the surface, even if cometary.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Chyba, C. F.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Publication Information
Publication: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F
Subject Category
Accession Number
Distribution Limits
Work of the US Gov. Public Use Permitted.

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