SWAS Observations of Comet 9P/Tempel 1 and Deep Impact

On 4 July 2005 at 5:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet (A'Hearn et al. 2005). The 370 kg impactor collided with the sunlit side of the nucleus with a relative velocity of 10.2 km s$^{-1}$. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the $1_{10}-1_{01}$ ortho-water ground-state rotational transition in comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before the impact.