February 2, 2006

Deep Impact probe shows ice on comet’s surface

WASHINGTON (Reuters) - Comet Tempel 1, the target of NASA's
Deep Impact space probe, has three patches of ice on its
surface, but most of the frozen water probably lurks deeper
inside, scientists reported on Thursday.

This marks the first time ice has been detected on the
nucleus, or solid body, of any comet, researchers reported in
the online version of the journal Science.

Deep Impact slammed into Tempel 1 last July 4, aiming to
collect data about the comet's heart.

Comets are of particular interest because they are believed
to be made up of the leftover debris from the gas, dust, rocks
and ice that formed the outer planets in our solar system some
4.6 billion years ago.

Scientists have long known that comets contain substantial
amounts of ice, but before Deep Impact, they did not know how
ice was distributed throughout the comet's nucleus.

Some astronomers believe comets "seeded" Earth with some of
the water and carbon-based molecules that make up living

The three small patches of ice on Tempel 1's surface are
not enough to account for the water vapor in the cloud of gas
and dust that surrounds the comet's nucleus, Deep Impact
scientists said in a statement.

"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 Michael A'Hearn of the
University of Maryland, the project's principal investigator.

The surface ice was detected by analysis of observations
made by the probe before it crashed into the comet. The crash
itself sent ice and water vapor blasting off the comet, and
analysis of this ejected material found that it must have come
from ice located close to, but not on, the comet's surface.