Visible and near-infrared (approximately 0.3 to 4.0 microns) spectroscopy has been successfully employed since the early 1970 s to infer the surface compositions of asteroids. Spectroscopic observations in the thermal infrared (approximately 5 to 40 microns) are similarly promising. Silicate spectra in this range are dominated by Si-O stretch and bend fundamentals, and other minerals have similarly diagnostic bands. Observations in this spectral range are difficult from the ground due to strong telluric absorptions and background emission. Nevertheless, spectral structure has been detected on a few asteroids in the 8 to 14-micron range from the ground, as well as from orbit with the ISO satellite. The Spitzer Space Telescope can observe asteroids with much higher sensitivity over a broader wavelength range than is possible from the ground or was possible with ISO. We present results of measurements of asteroids with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope
