LAUSR

Abstract On approach to comet 9P/Tempel 1, Deep Impact observed about one dozen natural outbursts. One of the largest occurred on 2 July 2005 and was also captured by Deep Impact's infrared spectrometer, HRI-IR. HRI-IR operates between 1.05 and 4.86 µm, allowing it to detect H 2 O (2.67 µm) and CO 2 (4.27 µm) emission bands simultaneously. In the hours leading up to the outburst, both H 2 O and CO 2 behaved quiescently, consistent with previously published studies. During the outburst, CO 2 abundance increased by 40% while H 2 O abundance stayed constant. No additional species were detectable during the outburst. The distribution of CO 2 during the outburst is correlated with that of the dust, observed at the same time in the visible. The abundance of CO 2 returned to quiescent levels within 3.6 h of outburst onset. A slight enhancement in H 2 O was observed well after the outburst, though this does not appear to be correlated with the outburst. From this analysis, it is likely that CO 2 was a driver of the 2 July 2005 outburst and that H 2 O was not.