COLLEGE PARK, Md. - NASA's Deep Impact spacecraft have 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. (See a movie of the outburst on the web at
http://www.newsdesk.umd.edu/scitech/DI/outburst.cfm ) The
outburst, which was detected as a dramatic brightening of the
comet on June 22, is the second of two such events observed in
the past two weeks. A smaller outburst was seen on June 14 by
ground-based observers, the Hubble Space Telescope and Deep
Impact. "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 astronomer Michael A'Hearn, who leads 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 double