Statistics
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.486b&link_type=abstract
Meteoritics, vol. 30, no. 5, page 486
Statistics
6
Achondrites, Basaltic, Asteroid Belt, Aubrites, Chondrites, Ordinary, Diogenites, Eucrites, Howardites, Spectral Reflectance, Vesta
Scientific paper
Historically, the path linking telescopic measurements of asteroids with laboratory measurements of meteorites has been an arduous one full of dead ends and dark passages. However some recent successes are beginning to clear and illuminate the path. Largely these successes have come about through advances in astronomical instrumentation and dedicated surveys of main-belt asteroids down to sizes substantially smaller than what had been previously observed. In addition, the most immediate precursor precursor population to meteorites, the near-Earth asteroids, are becoming more thoroughly studied. Three new links appear to have been forged. The strongest is the previously debated link between Vesta and the HED meteorites [1,2,3]. In a new survey of small (diameter < 20 km) main-belt asteroids, Binzel and Xu [4] found 20 which have visible spectra matching that which was previously unique to Vesta and the HED meteorites. While most appeared dynamically clustered around Vesta, eight of the discovered Vesta-like asteroids bridged the orbital space between Vesta and the 3:1 Jovian resonance -- a dynamical escape hatch to the inner solar system. Thus the observations demonstrate a complete delivery route for fragments from Vesta to the Earth, implying strong confidence that HED meteorites are derived from Vesta. The broad implications are that Vesta is now the fourth planetary body for which we have known samples, thus opening a new field for meteoritics and planetary science -- the geology of Vesta. A second, but more tentative link, is the discovery [5] of at least one small main-belt asteroid, 3628 Boznemcova, whose spectrum resembles ordinary chondrite meteorites. Previously, only one Earth-crossing asteroid (1862 Apollo) appeared to provide an asteroid spectral analog to these most common meteorites. Unfortunately the discovery of just one small main-belt ordinary chondrite-like asteroid out of about 1000 surveyed does not resolve issues such as whether space weathering is responsible for disguising the ordinary chondrite asteroids. A third interesting link is that between the aubrites and a spectrally similar asteroid, 3103 Eger. Gaffey et al. [6] note that the orbital intersections between Earth and Eger would give rise to the observed time-of-day fall statistics for the aubrites. They further cite the limited number of near-Earth asteroids having aubrite-like spectra and the clustering of aubrite cosmic ray exposure ages as strong suggestions for forging this new link. Continued spectroscopic surveys of asteroids, particularly among the most immediate meteorite source bodies -- small near-Earth asteroids, provide exciting promise for further success. References: [1] McCord T. B. et al. (1970) Science, 168, 1445. [2] M. J. Drake (1979) in Asteroids (T. Gehrels, ed.), pp. 765-782, Univ. of Arizona, Tucson. [3] Wetherill G. W. (1987) Philos. Trans. R. Soc. London, A323, 323. [4] Binzel R. P. and Xu S. (1993) Science, 260, 186. [5] Binzel R. P. et al. (1993) Science, 262, 1541. [6] Gaffey M. J. et al. (1992) Icarus, 100, 95.
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