37th DPS Meeting, 4-9 September 2005
Session 15 Asteroid Physical Studies
Poster, Monday, September 5, 2005, 6:00-7:15pm, Music Recital Room

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[15.07] Thermal Emission Spectroscopy of Asteroids with the Spitzer Space Telescope

J. P. Emery (NASA Ames / SETI Institute), D. P. Cruikshank (NASA Ames Research Center), J. Van Cleve (Ball Aerospace)

Several objects classified as asteroids have orbits that are dynamically similar to those of comets. These may be comets that have devolatilized by repeated passages through the inner Solar System. Reflectance spectroscopy in the vis-NIR cannot distinguish between devolatilized comets and low albedo asteroids (C-, P-, D-type asteroids); both sets of objects have low albedos and featureless spectra in the vis-NIR. In fact, the compositions of low albedo asteroids themselves are uncertain for this reason. Our observing program undertakes a spectroscopic study of 55 asteroids in the mid-infrared in order to better understand possible links between asteroids and comets. The asteroids observed so far sample the S, C, P, D, and M taxonomic classes and include Near Earth, Main Belt, and Trojan asteroids. The Infrared Spectrograph (IRS) on the Spitzer Space Telescope measures spectra over the range 5.2 \neg 38 \mum. This spectral range contains the Si-O stretch and bend fundamental vibrational bands, the positions and shapes of which are very diagnostic of silicate mineralogy. The thermal emission peak of most asteroids also occurs in this spectral range, which, along with the broad wavelength coverage, allows assessment of thermophysical properties of the surfaces, especially if physical properties (size, albedo, rotation state) are already known. Whereas most asteroids can be satisfactorily described by models with a thermal inertia of zero, several asteroids require a significant thermal inertia, implying less well-developed regoliths. There is significant diversity of spectral shape among the asteroids. Emissivity maxima near 10 and 20 \mum are strongest in the low albedo Trojan asteroids, but are also present, though weaker, in some (but not all) of the other asteroids. We will discuss potential implications of these new data for surface composition and physical and thermal properties of these objects.

The author(s) of this abstract have provided an email address for comments about the abstract: jemery@mail.arc.nasa.gov

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Bulletin of the American Astronomical Society, 37 #3
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