Spitzer Observations of the Dust Coma and Nucleus of 29P/Schwassmann-Wachmann 1

We obtained thermal images and spectra of comet and Centaur object 29P/Schwassmann-Wachmann 1 in late 2003 November. Images at 8, 24, and 70 μm reveal an extensive coma. At 24 μm the coma extends at least 8' from the nucleus and exhibits a single jet. The dust production rate is estimated as <~50 kg s^-1. The 24 to 70 μm color temperature of the coma is 160 K. The debris trail is also detected at 24 μm and has an optical depth of ~(7+/-3)×10^-9. Thermal models fitted to photometry at 8, 24, and 70 μm indicate a nuclear radius of 27+/-5 km, larger than all previous size estimates, and a geometric albedo of 0.025+/-0.01, lower than any other Centaur object, but consistent with other comets. Analysis of the jet morphology indicates a rotation period in excess of 60 days. The spectra reveal features at 11.3 and 34 μm, which are tentatively identified as emission from olivine, including forsterite. This is the first identification of the minerology of the dust emitted by a Centaur object.