2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 12
Presentation Time: 4:25 PM


SUNSHINE, Jessica, Astronomy, University of Maryland, Computer and Space Sciences Building, Colleg Park, MD 20742, BUS, Schelte, Institute for Astronomy, University of Hawaii, Hilo, HI 96720, CORRIGAN, Catherine, Applied Physics Lab, Johns Hopkins University, Laurel, MD 20723 and MCCOY, Timothy J., Mineral Sciences, Smithsonian Institution, Washington, DC 20560-0119, jess@astro.umd.edu

Melting models indicate that the composition and abundance of olivine systematically co-vary and are therefore excellent petrologic indicators. However, heliocentric distance, and thus surface temperature, has a significant effect on the spectra of olivine-rich asteroids. We show that composition and temperature complexly interact spectrally, and must be simultaneously taken into account in order to infer olivine composition accurately.

Using near-infrared data obtained at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea with SpeX, a low- to medium-resolution near-infrared spectrograph (0.8 to 2.5 µm) and pre-existing visbile spectra we examine the spectra of olivine dominated asteroids. We find that most (7/9) of the olivine-dominated asteroids are magnesian and thus likely sampled mantles differentiated from ordinary chondrite sources (e.g., pallasites). However, two other olivine-rich asteroids (289 Nenetta and 246 Asporina) are found to be more ferroan. Melting models show that partial melting cannot produce olivine-rich residues that are more ferroan than the chondrite precursor from which they formed. Thus, even moderately ferroan olivine must have non-ordinary chondrite origins, and therefore likely originate from oxidized R chondrite or melts thereof, which reflect variations in nebular composition within the asteroid belt. This is consistent with the meteoritic record in which R chondrites and brachinites are rare relative to pallasites.