NASA’s Deep Impact Films Earth As an Alien World

    COLLEGE PARK, Md., July 17 /EMWNews/ -- 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 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