Observing Silicate-Rich Asteroids in Technicolor: Detailed Compositional Constraints from SpeX.

Details Observing Silicate-Rich Asteroids in Technicolor: Detailed Compositional Constraints from SpeX. Observing Silicate-Rich Asteroids in Technicolor: Detailed Compositional Constraints from SpeX.

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p51c..06s&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P51C-06

Mathematics

Logic

6000 Planetology: Comets And Small Bodies, 6008 Composition, 6061 Remote Sensing

Scientific paper

We have recently begun a new survey of sili-cate-rich asteroids using SpeX, a low- to medium-resolution infrared spectrograph, at the Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii [1]. In its low-resolution mode (R approx.100), SpeX can produce spectra of faint asteroids from 0.8 to 2.5 microns with S/N comparable to data typically collected with visible wavelength CCDs. The SpeX data have been combined with visible CCD data measured during the SMASSII survey [2] to produce high S/N (often greater than100) spectra from 0.44 to 2.5 microns for several asteroids. This rich dataset includes subtle spectral signatures that we have analyzed with the Modified Gaussian absorption band model [3]. Among our results are clear unambiguous evidence for the presense of both high- and low-calcium pyroxene (HCP and LCP) as well as olivine and plagioclase. The quality of these data allow us to use the proportion of HCP relative to LCP, to constrain the petrologic history of these bodies. Very primitive bodies (e.g. primitive achondrites) have less than 10 percent HCP, while moderately evolved bodies (e.g. ordinary chondrites) have 15-20 percent HCP, and highly evolved bodies (e.g. basaltic achondrites) have more than 25 percent of their pyroxene as HCP. Our current dataset contains several asteroids, including members of the Merxia and Agnia families, with spectra that show little to no evidence for olivine, but instead are dominated by pyroxene absorptions and include significant (more than 40 percent) proportions of HCP. This HCP content implies a history of partial melting and silicate differentiation. As such we are actively examining smaller members of the Agnia and Merxia families to futher constrain the petrologic history of these bodies. References: [1] Rayner, J. T. et al. (1998) Proc. SPIE, 3354, 468-479. [2] Bus, S. J. et al. (2002) Icarus, 158, 106-145. [3] Sunshine, J. M. et al. (1990) JGR, 95, 6955-6966.

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