Submillimeter Wave Astronomy Satellite Observations of Comet 9P/Tempel 1

We present observations of the $1_{10}-1_{01}$ ortho-water ground-state rotational transition in comet 9P/Tempel 1 made with the NASA Submillimeter Wave Astronomy Satellite (SWAS). The SWAS monitoring covered a 3-month period from June to August 2005 and included observations of the comet’s activity during the collision of the Deep Impact spacecraft with the nucleus on 4 July 2005. No excess emission from the material ejected by the impactor was detected and we derive an upper limit of $1.8× 10^7$ kg on the vaporized water ice. However, the water production rate of the comet shows large natural variations of up to a factor of three throughout the 3-month monitoring period. The total amount of water vaporized between 5 June and 1 September 2005 is $4.5× 10³⁴$ molecules ($∼ 1.3× 10^9$ kg) and we estimate that 9P/Tempel 1 has lost as much as $N∼ 10³⁵$ molecules during its 2005 apparition.