NASA's Deep Impact Begins Hunt for Alien Worlds

Contact: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov

Nancy Neal-Jones 301-286-0039
NASA Goddard Space Flight Center, Greenbelt, Md.
Nancy.N.Jones@nasa.gov

Lee Tune 301-405-4679
University of Maryland, College Park
ltune@umd.edu

Press Release: 2008-021 February 7, 2008

NASA's Deep Impact Begins Hunt For Alien Worlds

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 Michael A'Hearn,
directed the spacecraft to begin these observations Jan. 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 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 Earth in visible and infrared wavelengths,
allowing comparisons with future discoveries of Earth-like planets around other stars.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages Epoxi for NASA's Science
Mission Directorate, Washington. The University of Maryland is the Principal
Investigator institution. NASA Goddard leads the mission's exosolar planet observations.
The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder,
Colo.

For information about Epoxi, visit http://www.nasa.gov/epoxi . More information about
JPL is at www.jpl.nasa.gov . More information about NASA programs is at

www.nasa.gov .

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