A Spitzer IRS Survey Of Hydrated and Non-Hydrated M Asteroids: Preliminary 5-13 Micron Results

Details A Spitzer IRS Survey Of Hydrated and Non-Hydrated M Asteroids: Preliminary 5-13 Micron Results A Spitzer IRS Survey Of Hydrated and Non-Hydrated M Asteroids: Preliminary 5-13 Micron Results

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.7104l&link_type=abstract

American Astronomical Society, DPS meeting #38, #71.04; Bulletin of the American Astronomical Society, Vol. 38, p.626

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Scientific paper

We are surveying the thermal emission spectra of 27 class M asteroids using the Spitzer Infrared Spectrograph (IRS; 5.2-38 microns). Although the visible and near-IR spectra of these asteroids are nearly featureless, ten of these asteroids are now known to have hydration features at 3 microns that are absent in the spectra of 15 others [1]. Mid-IR spectroscopy can reveal thermophysical and compositional information not available in the near-infrared.
Preliminary analysis of the SL1 (7.5-14.5 microns) module spectra of 15 asteroids (5 hydrated, 8 non-hydrated, two unknown) has been done by fitting the spectra with the asteroid standard thermal model ["STM"; e.g. 2], allowing the maximum temperature and radius to float. In the STM, the asteroids' thermophysical properties are summarized in a "beaming parameter" eta, which is related to the maximum temperature. Eta increases with thermal inertia and decreases with surface roughness.
For the five hydrated M asteroids, the parameter eta ranged from 0.81 (77 Frigga) to 1.06 (135 Hertha) with an average of 0.95. The eta values of the non-hydrated M asteroids ranged from 1.00 (857 Glasenappia) to 1.29 (216 Kleopatra) with an average of 1.15. Although the sample size is still small, both values are significantly higher than the "standard" asteroid eta value of 0.756. The differences between them suggest that M asteroids that lack the 3-micron hydration feature have significantly higher thermal inertias than those that have it, suggesting that they have either a better consolidated surface or more thermally conductive surface materials.
Calibration work on SL1 and the remaining IRS modules is still in progress.
This work is supported by Spitzer GO program 20481.
[1] Rivkin et al. 2000, Icarus 145, 351. [2] Lebofsky and Spencer 1989,in Asteroids II.

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