December 14, 2007

Deep Impact has New Mission for New Year

A former comet-slamming
spacecraft will swing by Earth on New Year's Eve before starting a
two-and-a-half-year journey to Comet Hartley 2.

Deep Impact will first spend six months using the larger of its
two telescopes to search for Earth-sized planets around five candidate stars. The
second part of its extended mission involves a flyby of Hartley 2 that allows
close observations of the comet's features.

"It's exciting that we can send the Deep Impact
spacecraft on a new mission that combines two totally independent science
investigations, both of which can help us better understand how solar systems
form and evolve," said Michael A'Hearn, Deep Impact leader and University of Maryland
astronomer, in a statement about the spacecraft's new EPOXI mission.

NASA originally gave the go-ahead for the Deep Impact
spacecraft to investigate
Comet Boethin
, but scientists eventually realized they could not identify
the comet and its orbit in time to plan the mission flyby of Earth. The
spacecraft will use the planet's pull of gravity to redirect itself toward Comet Hartley 2 on December 31, 2007.

Deep Impact made history on July 4, 2005 when it smashed
a probe into Comet Tempel
. The resulting data differed greatly from what scientists
found on previous comet missions Deep Space 1 and Stardust.

"One of the great surprises of comet explorations has
been the wide diversity among the different cometary surfaces imaged to
date," said A'Hearn. "We want a close look at Hartley 2 to see if the
surprises of Tempel 1 are more common than we thought, or if Tempel 1 really is

The Deep Impact eXtended Investigation (DIXI) will follow up
on those earlier findings not by smashing objects into Comet Hartley 2, but
by mapping outbursts of gas from the comet surface, looking for water
ice, and analyzing the cloud of gas and dust surrounding the comet.

However, starting in late January, the spacecraft will first
focus on detecting alien
in the Extrasolar Planet Observations and Characterization (EPOCh)
phase of its two-part mission.

Many extrasolar or alien planets normally remain hidden
because of the glaring light from their stars. Deep Impact's telescope can
detect planets by subtracting the light of a star alone from the combined light
of both the star and its planet.

The mission will observe five nearby stars where large, Jupiter-like
planets were already discovered. Deep Impact may detect neighboring
planets by watching for any gravitational pulls on the known planets' orbits.

The total journey – starting from December 31, 2007 to the closest comet encounter on October 11, 2010 – will be roughly 1.6 billion miles
or some 18 times the distance from the Earth to the sun. The spacecraft will
need three trips around the sun before it can intercept Comet Hartley 2.