Spectral Trends of S-Class Asteroids with Size and Dynamical Population

Details Spectral Trends of S-Class Asteroids with Size and Dynamical Population Spectral Trends of S-Class Asteroids with Size and Dynamical Population

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1016h&link_type=abstract

American Astronomical Society, DPS meeting #28, #10.16; Bulletin of the American Astronomical Society, Vol. 28, p.1099

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The majority of near-Earth asteroids (NEAs) whose taxonomic types are known belong to Tholen's S-class (Tholen, 1984). The reflectance spectra of S-class asteroids show absorption bands due to pyroxene or olivine or both, and the continuum slopes are moderately red. Compared to larger, main-belt asteroids, the NEAs have deeper absorption bands, which may be due to their surfaces having little or no regolith. Thus, we expect that the smaller asteroids will better match meteorite spectra than main-belt asteroids of the same composition. Visible and near-infrared spectra have been obtained for several S-class NEAs: 4179 Toutatis, 4954 Eric, 4953 1990 MU, 1991 JX, 1865 Cerberus, and 1993 MF. Similar data for larger NEAs 1036 Ganymed and 1627 Ivar, along with many main-belt asteroids (Bell et al. 1988), are compared to the smaller object spectra and with meteorite analogs. The compositional diversity and spectral contrast of the smaller objects are both increased compared to larger S-class asteroids. Xu et al. (1995) obtained this same result using a smaller spectral range comparing small main-belt objects to the larger ones in the same taxonomic classes. The continuum slope of smaller NEAs is much redder than that of meteorite spectra, indicating either a compositional difference, or some space weathering effect. Laboratory experiments (e.g. Clark et al., 1992) have not been able to reproduce the continuum reddening with heating or simulated shock effects. If the systematic spectral differences between large (> 20 km) main-belt asteroids and meteorites is not primarily compositional, but is some combination of weathering and regolith affecting the reflectance spectrum, the small NEA spectra should be intermediate between these end-members. These observations represent a statistically significant sample over a wide enough spectral range to determine the trends. We will put constraints on the processes that can produce these trends to better understand the differences between meteorite and asteroid spectra. Without this link, the application of the detailed chemistry of meteorites to asteroid formation is premature.

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