Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..453v&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 453
Computer Science
2
Asteroids, Meteorites, Orbits
Scientific paper
A recent study of Earth-approaching asteroids concluded that some newly discovered asteroids may comprise a different population from previously discovered Earth-crossers [1]. The orbits of these objects generally have both perihelia and aphelia close to 1 AU, relatively low eccentricities, and inclinations of up to 30 degrees. We modeled the orbital evolution of particles using an Opik-type model [2] to test possible modes of origin of these asteroids. We considered that the most likely candidates were ejecta from the Earth or Moon, from Mars, and from the region of the 3:1 commensurability with Jupiter. The Earth/Moon system seems a likely source because of the similarity of the asteroidal orbits to Earth's. An orbital evolution study of the exchange of material between planets, however, indicates that planetary ejecta tend strongly to move inward toward the Sun instead of remaining close to the planet of origin or moving outward [2]. This, plus the fact that the SNC meteorites apparently came from Mars to Earth, motivated us to include Mars as a possible origin site. Lastly, for completeness, we included calculations of the evolution of material from the asteroid belt. For this last part, we relied on the work of Wisdom [3], which indicates that asteroids with orbits near the 3:1 commensurability with Jupiter may be perturbed into either Mars- or Earth- crossing orbits on relatively short timescales, mainly by an increase in the orbital eccentricities. This follows the approach of Wetherill [4]. For orbital evolution times of roughly 50 Ma or less, the best fit to the observations is given by Earth/Moon ejecta and by Earth-crossing bodies from the main asteroid belt, and the model cannot distinguish which of these is more likely. For longer times, however, these two populations both evolve away from orbits similar to that of the Earth. The Mars-crossing asteroidally derived bodies do not evolve nearly so much as those in the first two populations, primarily because the smaller size of Mars makes it a less efficient perturber of orbits; very few of these bodies ever become Earth-crossers. The particles ejected from Mars directly behave somewhat differently. Although they are not scattered as efficiently as the Earth/Moon ejecta or the Earth-crossing asteroidal bodies, a significant fraction of them assume Earth-crossing orbits of low to moderate eccentricity for evolution times of roughly 50 Ma or more. In summary, if the Rabinowitz objects are young (<=50 Ma) then they are likely to be either Earth/Moon ejecta or former main belt asteroids that were perturbed into eccentric orbits by chaotic effects at the 3.1 commensurablity. If theses objects are older than ca. 50 Ma, however, they are more likely to be Mars ejecta, and may represent the source of the SNC meteorites. References: [1] Rabinowitz D. L. (1993) Ap. J., in press. [2] Melosh H. J. and Tonks W. B. (1993), this volume. [3] Wisdom J. (1985) Nature, 315, 731. [4] Wetherill G. W. (1985) Meteoritics, 20, 1.
Melosh Henry Jay
Vickery Ann M.
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