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.
Image right: Deep Impact view of Tempel 1. Image credit: NASA/JPL-Caltech.
+ Tempel 1 movie
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.
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
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,"
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."
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.
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