NASA's Deep Impact Begins Hunt for Alien Worlds

GREENBELT, Md., Feb. 7 /PRNewswire-USNewswire/ -- NASA's Deep Impact
spacecraft is aiming its largest telescope at five stars in a search for
alien (exosolar) planets as it enters its extended mission, called EPOXI.

Deep Impact made history when the mission team directed an impactor
from the spacecraft into comet Tempel 1 on July 4, 2005. NASA recently
extended the mission, redirecting the spacecraft for a flyby of comet
Hartley 2 on Oct. 11, 2010.

As it cruises toward the comet, Deep Impact will observe five nearby
stars with "transiting exosolar planets," so named because the planet
transits, or passes in front of, its star. The EPOXI team, led by
University of Maryland astronomer Dr. Michael A'Hearn, directed the
spacecraft to begin these observations January 22. The planets were
discovered earlier and are giant planets with massive atmospheres, like
Jupiter in our solar system. They orbit their stars much closer than Earth
does the sun, so they are hot and belong to the class of exosolar planets
nicknamed "Hot Jupiters."

However, these giant planets may not be alone. If there are other
worlds around these stars, they might also transit the star and be
discovered by the spacecraft. Deep Impact can even find planets that don't
transit, using a timing technique. Gravity from the unseen planets will
pull on the transiting planets, altering their orbits and the timing of
their transits.

"We're on the hunt for planets down to the size of Earth, orbiting some
of our closest neighboring stars," said EPOXI Deputy Principal Investigator
Dr. Drake Deming of NASA's Goddard Space Flight Center in Greenbelt, Md.
EPOXI is a combination of the names for the two extended mission
components: the exosolar planet observations, called Extrasolar Planet
Observations and Characterization (EPOCh), and the flyby of comet Hartley
2, called the Deep Impact eXtended Investigation (DIXI). Goddard leads the
EPOCh component.

More than 200 exosolar planets have been discovered to date. Most of
these are detected indirectly, by the gravitational pull they exert on
their parent star. Directly observing exosolar planets by detecting the
light reflected from them is very difficult, because a star's brilliance
obscures light coming from any planets orbiting it.

However, sometimes the orbit of an exosolar world is aligned so that it
eclipses its star as seen from Earth. In these rare cases, called transits,
light from that planet can be seen directly.

"When the planet appears next to its star, your telescope captures
their combined light. When the planet passes behind its star, your
telescope only sees light from the star. By subtracting light from just the
star from the combined light, you are left with light from the planet,"
said Deming, who is leading the search for exosolar worlds with Deep
Impact. "We can analyze this light to discover what the atmospheres of
these planets are like."

Deep Impact will also look back to observe the Earth in visible and
infrared wavelengths, allowing comparisons with future discoveries of
Earth-like planets around other stars.

The University of Maryland is the Principal Investigator institution,
leading the overall EPOXI mission, including the flyby of comet Hartley 2,
called the Deep Impact eXtended Investigation (DIXI). NASA Goddard leads
the exosolar planet observations, called Extrasolar Planet Observations and
Characterization (EPOCh). EPOXI is a combination of the names for these two
extended mission components. NASA's Jet Propulsion Laboratory, Pasadena,
Calif., manages EPOXI for NASA's Science Mission Directorate, Washington.
The spacecraft was built for NASA by Ball Aerospace & Technologies Corp.,
Boulder, Colo.

For information about EPOXI, visit: http://www.nasa.gov/epoxi