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Date: Tue, 28 Jun 2005 15:00:21 -0700
From: NASA Jet Propulsion Laboratory <>
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Subject: NASA's Deep Impact Craft Observes Major Comet 'Outburst'

PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011

DC Agle (818) 393-9011
Jet Propulsion Laboratory, Pasadena, Calif.

Dolores Beasley (202) 358-1753
NASA Headquarters, Washington

Lee Tune (301) 405-4679
University of Maryland, College Park

News Release: 2005-104					 June 28, 2005

NASA's Deep Impact Craft Observes Major Comet 'Outburst'

NASA's Deep Impact spacecraft observed a massive, short-lived outburst of ice or other
particles from comet Tempel 1 that temporarily expanded the size and reflectivity of the
cloud of dust and gas (coma) that surrounds the comet nucleus.

The outburst was detected as a dramatic brightening of the comet on June 22. It is the
second of two such events observed in the past two weeks. A smaller outburst also was
seen on June 14 by Deep Impact, the Hubble Space Telescope and by ground based

"This most recent outburst was six times larger than the one observed on June 14, but
the ejected material dissipated almost entirely within about a half day," said University
of Maryland College Park astronomer Michael A'Hearn, principal investigator for the
Deep Impact mission. A'Hearn noted that data from the spectrometer aboard the
spacecraft showed that during the June 22 outburst the amount of water vapor in the
coma doubled, while the amount of other gases, including carbon dioxide, increased
even more.

A movie of the cometary outburst is available on the Internet at .

"Outbursts such as this may be a very common phenomenon on many comets, but they
are rarely observed in sufficient detail to understand them because it is normally so
difficult to obtain enough time on telescopes to discover such phenomena," A'Hearn
said. "We likely would have missed this exciting event, except that we are now getting
almost continuous coverage of the comet with the spacecraft's imaging and
spectroscopy instruments."

Deep Impact co-investigator Jessica Sunshine, with Science Applications International
Corporation, Chantilly, Va., agreed that observing such activity twice in two weeks
suggests outbursts are fairly common. "We must now consider them as a significant
part of the processing that occur on comets as they heat up when approaching the sun,"
she said.

Comet Tempel 1 is near perihelion, or the point in its orbit at which it is closest to the

"This adds to the level of excitement as we come down to the final days before
encounter," said Rick Grammier, Deep Impact project manager at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "But this comet outburst will require no
modification to mission plan and in no way affects spacecraft safety."

Deep Impact consists of a sub-compact-car-sized flyby spacecraft and an impactor
spacecraft about the size of a washing machine. The dual spacecraft carries three
imaging instruments, two on the flyby spacecraft and one on the impactor. A
spectrometer on the flyby spacecraft uses the same telescope as the flyby's high-
resolution imager.

The final prelude to impact will begin early on July 3, 24 hours before the 1:52 a.m.
EDT July 4th impact, when the flyby spacecraft releases the impactor into the path of
the comet. Like a copper penny pitched up into the air just in front of a speeding
tractor-trailer truck, the 820-pound impactor will be run down by the comet, colliding
with the nucleus at a closing speed of 23,000 miles per hour. Scientists expect the
impact to create a crater several hundred feet in size; ejecting ice, dust and gas from the
crater and revealing pristine material beneath. The impact will have no significant
affect on the orbit of Tempel 1, which poses no threat to Earth.

Nearby, Deep Impact's "flyby" spacecraft will use its medium and high resolution
imagers and infrared spectrometer to collect and send to Earth pictures and spectra of
the event. The Hubble and Spitzer Space Telescopes, the Chandra X-ray Observatory,
and large and small telescopes on Earth also will observe the impact and its aftermath.

The University of Maryland, College Park, conducts overall mission science for Deep
Impact that is a Discovery class NASA program. NASA's Jet Propulsion Laboratory
handles project management and mission operations. The spacecraft was built for
NASA by Ball Aerospace and Technologies Corporation, Boulder, Colo.


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