NASA's Deep Impact Films Earth as an Alien World

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Lee Tune 301-405-4679
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David L. Chandler 617-253-2704
Massachusetts Institute of Technology, Cambridge, Mass.
dlc1@MIT.EDU

NEWS RELEASE: 2008-137 July 17, 2008

NASA's Deep Impact Films Earth as an Alien World

PASADENA, Calif. -- NASA's Deep Impact spacecraft has created a video of the moon
transiting (passing in front of) Earth as seen from the spacecraft's point of view 50
million kilometers (31 million miles) away. Scientists are using the video to develop
techniques to study alien worlds.

"Making a video of Earth from so far away helps the search for other life-bearing planets
in the Universe by giving insights into how a distant, Earth-like alien world would appear
to us," said University of Maryland astronomer Michael A'Hearn, principal investigator
for the Deep Impact 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 Nov. 4, 2010.

Epoxi is a combination of the names for the two extended mission components: a search
for alien (extrasolar) planets during the cruise to Hartley 2, called Extrasolar Planet
Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the
Deep Impact eXtended Investigation (DIXI).

During a full Earth rotation, images obtained by Deep Impact at a 15-minute cadence
have been combined to make a color video. During the video, the moon enters the frame
(because of its orbital motion) and transits Earth, then leaves the frame. Other spacecraft
have imaged Earth and the moon from space, but Deep Impact is the first to show a
transit of Earth with enough detail to see large craters on the moon and oceans and
continents on Earth.

"To image Earth in a similar fashion, an alien civilization would need technology far
beyond what Earthlings can even dream of building," said Sara Seager, a planetary
theorist at the Massachusetts Institute of Technology, Cambridge, Mass., and a co-
investigator on Epoxi. "Nevertheless, planet-characterizing space telescopes under study
by NASA would be able to observe an Earth twin as a single point of light -- a point
whose total brightness changes with time as different land masses and oceans rotate in
and out of view. The video will help us connect a varying point of planetary light with
underlying oceans, continents, and clouds -- and finding oceans on extrasolar planets
means identifying potentially habitable worlds." said Seager.

"Our video shows some specific features that are important for observations of Earth-like
planets orbiting other stars," said Drake Deming of NASA's Goddard Space Flight Center
in Greenbelt, Md. Deming is deputy principal investigator for Epoxi, and leads the
EPOCh observations. "A 'sun glint' can be seen in the movie, caused by light reflected
from Earth's oceans, and similar glints to be observed from extrasolar planets could
indicate alien oceans. Also, we used infrared light instead of the normal red light to make
the color composite images, and that makes the land masses much more visible." That
happens because plants reflect more strongly in the near-infrared, Deming explained.
Hence the video illustrates the potential for detecting vegetated land masses on extrasolar
planets by looking for variations in the intensity of their near-infrared light as the planet
rotates.

The University of Maryland is the Principal Investigator institution,
leading the overall Epoxi mission, including the flyby of comet
Hartley 2. NASA Goddard leads the extrasolar planet observations.
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.

To see the video, visit:
http://www.nasa.gov/topics/solarsystem/features/Epoxi_transit.html

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