Carbon Monoxide in Comet 9P/Tempel 1 before and after theDeep ImpactEncounter

Abstract

One of the goals of the Hubble Space Telescope program to observe periodic comet 9P/Tempel 1 in conjunction with NASA's Deep Impact mission was to study the generation and evolution of the gaseous coma resulting from the impact. For this purpose, the Solar Blind Channel of the Advanced Camera for Surveys was used with the F140LP filter, which is sensitive primarily to the ultraviolet emission (≥1400 A) from the CO fourth positive system. Following the impact we detected an increase in brightness, which if all due to CO corresponds to 1.5 × 1031 molecules, or a mass of 6.6 × 105 kg, an amount that would normally be produced by 7-10 hours of quiescent outgassing from the comet. This number is ≤10% of the number of water molecules excavated and suggests that the volatile content of the material excavated by the impact did not differ significantly from the surface or near-subsurface material responsible for the quiescent outgassing of the comet.