June 28, 2005

Dolores Beasley
Headquarters, Washington 
(Phone: 202/358-1753)
DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/393-9011)

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

RELEASE: 05-167

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 observers. 

"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.

"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," he said.

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 Sun. 

"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," he added.

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.

To view a movie showing the cometary outburst on the Internet, visit: 

www.nasa.gov/deepimpact

	
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