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J. P. Emery (NASA Ames/SETI Institute), D. P. Cruikshank (NASA Ames), J. Van Cleve (Ball Aerospace), J. A. Stansberry (Univ. Arizona)
We will present thermal emission spectra of asteroids, Centaurs, and Kuiper Belt objects from the Infrared Spectrograph (IRS) on the Spitzer space telescope. To date, 15 of the 42 asteroids and 11 of the 17 KBOs/Centaurs in our programs have been observed. The asteroids observed so far sample the S, C, P, D, and M taxonomic classes and include Near Earth, Main Belt, and Trojan asteroids. Emissivity spectra are created by dividing the measured spectral energy distributions (SEDs) by models of the thermal continua. We use either a standard thermal model or a more advanced thermophysical model (includes thermal inertia, obliquity, and surface roughness), as applicable for each asteroid. These models describe the SEDs very well. The asteroid spectra typically include the full range of IRS (5.2 to 38 microns) and have spectral resolutions of 64-128 and ~600 for the low and high resolution modules, respectively. The most striking feature in these asteroid spectra is an emission plateau that extends over the range ~ 9.0 – 11.5 microns. This feature is strongest in the low albedo Trojan asteroids, but is also present, though weaker, in some (but not all) of the other asteroids. We compare these new data with laboratory spectra of meteorites and minerals. The KBO/Centaurs are colder and farther away, so they are fainter and their SEDs peak at longer wavelengths than the asteroids. Accordingly, most of these are only observable with the longer wavelength IRS modules (~15 – 38 microns with R ~ 64-128), and the resulting sensitivity is lower. For some of the KBO/Centaurs, the IRS data provide the first constraints on size and albedo, and we find albedos may be higher than anticipated. 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, 36 #4
© 2004. The American Astronomical Soceity.