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
Media contacts: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
Nancy Neal 301-286-0039
Goddard Space Flight Center, Greenbelt, MD
Lee Tune 301-405-4679
University of Maryland, College Park