Deep Impact : Excavating Comet Tempel

Introduction: On 4 July 2005, Deep Impact delivered 19 GJoules of kinetic energy to the nucleus of comet Tempel 1, taking numerous images and spectra of the comet before, during, and after the impact. The preliminary analysis of the data has already lead to significant, new understanding of cometary properties and behavior [1] and this talk will summarize the present state of our understanding with details of some results in related talks. Data Collected: Data from the impactor, all in the last 24 hours before impact, were limited to white-light images of successively smaller frames, taken with increasing frequency (1 per 2 sec at the end) as we approached the comet. These images provided, for example, a few-meter resolution image of the impact site. The multi-filter, high-resolution imager, near-infrared spectrometer, and multi-filter, medium resolution imager provided extensive coverage during two months of approach, detailed, high-frequency (every 65 msec) imaging of the impact event, and details of the nucleus and the ejecta both before and after closest approach until more than 2.5 days after impact. Although first results have been published [1], ongoing analysis is leading to a continuing series of new results, many of which are being presented in companion talks in this session. Nuclear Activity: The intense coverage during approach led to the detection of numerous outbursts, both from Deep Impact itself and also from both ground-based observatories [2] and HST [3]. Although not truly periodic, there was roughly one outburst per week, only some of which were large enough to have been seen from Earth if anyone was looking. The fact that many but not all of the outbursts are correlated with the nuclear rotational phase [1, 4] rules out exogenic causes, such as impacts or fluctuations in the solar wind or other solar activity, as causes of the outbursts. The outbursts that are correlated with rotational phase appear to arise from an area that is near sunrise at the time of the outbursts and they may be associated with the icy areas that have been identified on the surface [5]. This suggests migration of ice to the near-surface region which rapidly evaporates when heated by a very small amount of sunlight. Spectroscopy on approach showed unidentified spectral features during the one outburst that coincided with spectral measurements. Furthermore, the ambient coma showed clear evidence for