GALEX Observations of CS and OH Emission in Comet 9P/Tempel 1 During Deep Impact

Abstract

GALEX observations of comet 9P/Tempel 1 using the near ultraviolet (NUV) objective grism were made before, during and after the Deep Impact event that occurred on 2005 July 4 at 05:52:03 UT when a 370 kg NASA spacecraft was maneuvered into the path of the comet. The NUV channel provides usable spectral information in a bandpass covering 2000 - 3400 A with a point source spectral resolving power of approximately 100. The primary spectral features in this range include solar continuum scattered from cometary dust and emissions from OH and CS molecular bands centered near 3085 and 2575 A, respectively. In particular, we report the only cometary CS emission detected during this event. The observations allow the evolution of these spectral features to be tracked over the period of the encounter. In general, the NUV emissions observed from Tempel 1 are much fainter than those that have been observed by GALEX from other comets. However, it is possible to derive production rates for the parent molecules of the species detected by GALEX in Tempel 1 and to determine the number of these molecules liberated by the impact. The derived quiescent production rates are Q(H2O) = 6.4e27 molecules/s and Q(CS2) = 6.7e24 molecules/s, while the impact produced an additional 1.6e32 H2O molecules and 1.3e29 CS2 molecules, a similar ratio as in quiescent outgassing.