Office of University Communications
University of Maryland
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
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,