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Originally published in Science Express on 8 September 2005
Science 14 October 2005:
Vol. 310. no. 5746, pp. 258 - 264
DOI: 10.1126/science.1118923
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Research Articles

Deep Impact: Excavating Comet Tempel 1

M. F. A'Hearn,1* M. J. S. Belton,2 W. A. Delamere,3 J. Kissel,4 K. P. Klaasen,5 L. A. McFadden,1 K. J. Meech,6 H. J. Melosh,7 P. H. Schultz,8 J. M. Sunshine,9 P. C. Thomas,10 J. Veverka,10 D. K. Yeomans,5 M. W. Baca,9 I. Busko,11 C. J. Crockett,1 S. M. Collins,5 M. Desnoyer,10 C. A. Eberhardy,8 C. M. Ernst,8 T. L. Farnham,1 L. Feaga,1 O. Groussin,1 D. Hampton,12 S. I. Ipatov,1 J.-Y. Li,1 D. Lindler,13 C. M. Lisse,1,14 N. Mastrodemos,5 W. M. Owen, Jr.,5 J. E. Richardson,7,10 D. D. Wellnitz,1 R. L. White11

Deep Impact collided with comet Tempel 1, excavating a crater controlled by gravity. The comet's outer layer is composed of 1- to 100-micrometer fine particles with negligible strength (<65 pascals). Local gravitational field and average nucleus density (600 kilograms per cubic meter) are estimated from ejecta fallback. Initial ejecta were hot (>1000 kelvins). A large increase in organic material occurred during and after the event, with smaller changes in carbon dioxide relative to water. On approach, the spacecraft observed frequent natural outbursts, a mean radius of 3.0 ± 0.1 kilometers, smooth and rough terrain, scarps, and impact craters. A thermal map indicates a surface in equilibrium with sunlight.

1 University of Maryland, College Park, MD 20742, USA.
2 Belton Space Exploration Initiatives, Tucson, AZ 85716, USA.
3 Delamere Support Services, Boulder, CO 80301, USA.
4 Max-Planck-Institute for Solar System Research, Katlenburg-Lindau, D37191 Germany.
5 Jet Propulsion Laboratory, Pasadena, CA 91109, USA.
6 University of Hawaii, Honolulu, HI 96822, USA.
7 University of Arizona, Tucson, AZ 85721, USA.
8 Brown University, Providence, RI 02412, USA.
9 SAIC, Chantilly, VA 20151, USA.
10 Cornell University, Ithaca, NY 14853, USA.
11 Space Telescope Science Institute, Baltimore, MD 21218, USA.
12 Ball Aerospace and Technology Corporation, Boulder, CO 80301, USA.
13 Sigma Scientific, Greenbelt, MD 20771, USA.
14 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA.

* To whom correspondence should be addressed. E-mail: ma{at}astro.umd.edu

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