NASA's Deep
Impact spacecraft has made a movie of the moon passing in front of the Earth
from the probe's vantage point millions of miles away.
Astronomers
plan to use the
video to develop techniques to look for Earth-like worlds in other solar
systems.
"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 Michael A'Hearn of the University of Maryland and the principal investigator for the Deep Impact extended mission.
Deep
Impact, which sent an impactor into comet Tempel 1 on July 4, 2005, is
currently 31 million miles away from Earth on its way to a flyby of comet
Hartley 2 on Nov. 4, 2010.
During its
cruise to Hartley 2, Deep Impact
will be searching for extrasolar planets.
Deep Impact
took several images of the Earth during a full planetary rotation; these images
have been combined into a color video. During the video, the moon enters the
frame as it orbits the Earth and then is shown transiting, or passing in front
of, the Earth.
While other
spacecraft, including Voyager 1 and Galileo, have imaged Earth and the moon
from space, 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.
"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., and the deputy principal investigator for the
extended mission. "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."
The team used
infrared light to look at the Earth because plants reflect more strongly in the
near-infrared, so the video will help scientists evaluate the potential for
detecting vegetated land masses on alien planets.
Most of the
nearly
300 extrasolar planets that have been found to date are Jupiter-sized
behemoths, though a few "super-Earths," around four to nine times the
mass of our planet, were recently detected.
NASA is
currently studying planet-characterizing telescopes that would observe
extrasolar planets as a single point of light and would distinguish land masses
and oceans by changes in the total brightness, said planetary theorist Sara
Seager of MIT and a co-investigator on the Deep impact extended mission.
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