[meteorite-list] Ice Exists on Surface of Comet, But Most Lies Deeper (Deep Impact)

[Ron Baalke]

http://www.newsdesk.umd.edu/scitech/release.cfm?ArticleID=1213

Office of University Communications
University of Maryland

Contacts:
Lee Tune, 301-405-4679

For Immediate Release: February 2, 2006

Ice Exists on Surface of Comet, But Most Lies Deeper

COLLEGE PARK, Md. -- Scientists for Deep Impact, the University of 
Maryland-led NASA mission that made history when it smashed into a comet 
this past July 4th, have added another first to their growing list: the 
first finding of water ice on the surface of a comet.

By analyzing data and images taken prior to impact, Deep Impact scientists 
have detected water ice in three small areas on the surface of comet 
Tempel 1. This is the first time ice has been detected on the nucleus, or 
solid body, of a comet. The findings are published today in the online 
version of the journal Science.

"These results show that there is ice on the surface, but not very much 
and definitely not enough to account for the water we see in the 
out-gassed material that is in the coma [the cloud of gas and dust that 
surrounds the comet]," said lead author Jessica Sunshine of Science 
Applications International Corporation.

"These new findings are significant because they show that our technique 
is effective in finding ice when it is on the surface and that we can 
therefore firmly conclude that most of the water vapor that escapes from 
comets is contained in ice particles found below the surface," said Deep 
Impact Principal Investigator Michael A'Hearn of the University of 
Maryland.

Where's the Ice?

Through observations of ice grains and water vapor in the coma of comets, 
scientists have long known that "dirty snowballs," as comets are sometimes 
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.

"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. Li, 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. Yeomans, 
Jet Propulsion Laboratory; 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.

Deep Impact Slide Show,
     http://www.newsdesk.umd.edu/images/DeepImpact/DISlideShow.cfm