"Deep Impact: Excaving Comet Tempel 1"
S.I. Ipatov (University of Maryland, USA)
Abstract:
On 4 July 2005 Deep
Impact collided with comet Tempel 1, excaving a crater. Deep Impact
consisted of two fully functional spacecraft: an impacting spacecraft
weighting 364 kg and a flyby spacecraft for observing the impact and
relaying data from the impactor. There were three optical instruments on
both spacecraft: a high-resolution instrument (HRI) and a
medium-resolution instrument (MRI) on the flyby spacecraft, and an
impactor targeting sensor (ITS) mounted on the impactor. HRI has the
infrared (1.05 to 4.8 micron) spectrometer. The impact was also observed
by over 80 ground-based observatories and by several spacecraft (Rosetta,
Hubble Space Telescope, Chandra, Spitzer). Impact speed was 10.3 km/s. The
impact was oblique, 20 to 35 degrees from horizontal. Initial ejecta were
hot (>1000 kelvins). The fastest material was moving at ~5 km/s,
projected in the plane of the sky as seen from the spacecraft. The true
velocity is likely to have been 7 to 10 km/s. A large increase in organic
material occurred during and after the impact, with smaller changes in
carbon dioxide relative to water. Hydrogen cyanide (HCN) was identified in
the plume. The mean radius of the nucleus is estimated to have been 3.0±0.1
km, the longest dimension is 7.6 km and the shortest is 4.9 km. Albedo
variations are within 50% of an average of 0.04. The bulk density of the
nucleus is estimated at roughly 0.6 g cm-3. The derived
temperature varies from 260±6 K to 329±8 K on the sunlit side.
Observations of the comet before impact detected numerous brief outbursts
from the comet. Many of the outbursts were associated with an area near
local sunrise. Based on the images obtained during the flight, we studied
cosmic rays.