37th DPS Meeting, 4-9 September 2005
Session 38 Deep Impact II
Invited, Wednesday, September 7, 2005, 2:15-4:00pm, Music Concert Hall

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[38.05] The Deep Impact Experiment and the Physics of Impact Cratering

J.E. Richardson (Cornell University), H.J. Melosh (University of Arizona), Deep Impact Science Team

On July 4, 2005 the Deep Impact experiment produced an impact event on the surface of Comet 9P Tempel 1, using a 360 kg (primarily copper) impactor striking the comet at a velocity of 10.2 km/sec. In addition to images taken from the flyby spacecraft (500 km closest approach distance), images of the target were also returned from the impactor spacecraft, which show that the impactor hit the comet's surface at an oblique angle of roughly 60 degrees from the surface normal. The impactor struck the comet at an ideal location for viewing the cratering process by the flyby spacecraft both during the 800 second long post-impact imaging phase and during the ``look-back" imaging phase (beginning ~ 45 minutes after impact). Within a fraction of a second of impact, an incandescent vapor plume emerged from the impact site, cooling rapidly and moving away from the comet at a speed of ~ 5 km/sec. This vapor emission was followed by the emergence and rapid growth of a prominent, conical ejecta plume, indicating crater excavation flow. This ejecta plume was more opaque (composed of finer material) than predicted, obscuring clear observations of the impact crater itself (extraction efforts continue). However, the behavior of the plume during both it's growth and fallback stages is consistent with a gravity-scaled cratering event into a very weak (post-shock) target material. The expansion state of the plume during the look-back phase will also allow us to place constraints on the comet's gravity field (and by extension mass and density).

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.