As a comet approaches the Sun, it releases gas and dust forming a cloud (coma) that obscures the nucleus from view unless spacecraft can get very close. Deep Impact did just that.The Deep Impact science team used four types of data in their search for ice on the mostly coal black surface of Tempel 1.
First, images from Deep Impact's high resolution and medium resolution instruments (the HRI and MRI) showed three small regions that were about 30 percent brighter than surrounding areas. After scaling the images to the average brightness value of the nucleus, these three discrete areas on the nucleus where found to be brighter in the ultraviolet and darker in the near-infrared, a combination that is consistent with water ice. In addition, Sunshine's analysis of the spectra of light emitted and absorbed in those regions showed the distinctive spectral signature of water ice. The combination of the relative colors and the spectral signature make a powerful case that there is water ice at these specific locations on Tempel 1.
Using visual images and spectral mapping of the impact side of the surface of Tempel 1, the team found that the patches of surface ice represented only 0.5 percent of the total observed surface.
Team member Olivier Groussin, a University of Maryland research scientist, made a temperature map and combined it with the color map to show that two of the three ice patches regions were in colder regions of the nucleus. Stereo images show the largest area of ice to be a depression 80 meters below surrounding areas.
The University of Maryland, College Park, conducted the overall mission management for Deep Impact, which is a Discovery class NASA program. NASA's Jet Propulsion Laboratory (JPL) handled project management for the Deep Impact mission. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo.
"Water Ice on the Surface of Comet Tempel 1," J. M. Sunshine, Science Applications International Corporation (SAIC); M. F. A'Hearn, University of Maryland; O. Groussin, University of Maryland; J.-Y. Li2, University of Maryland; M. J. S. Belton, Belton Space Exploration Initiatives; W. A. Delamere, Delamere Support Services'; J. Kissel, Max-Planck-Institute for Solar System Research; K. P. Klaasen, Jet Propulsion Laboratory; L. A. McFadden, University of Maryland; K. J. Meech, University of Hawaii; H. J. Melosh, University of Arizona; P. H. Schultz, Brown University; P. C. Thomas, Cornell University; J. Veverka, Cornell University; D. K. Yeomans6, I. C. Busko, Space Telescope Science Institute; M. Desnoyer, Cornell University; T. L. Farnham, University of Maryland; L. M. Feaga, University of Maryland; D. L. Hampton, Ball Aerospace & Technology Corporation; D. J. Lindler, Sigma Scientific; C. M. Lisse, Applied Physics Laboratory, Johns Hopkins University; D. D. Wellnitz, University of Maryland. Published in Science Express, February 2, 2006.