NASA Aids First Characterization Of Super-Earth Atmosphere
WASHINGTON -- A team of astronomers, including two NASA Sagan Fellows, has made the first characterizations of a super-Earth's atmosphere by using a ground-based telescope. A super-Earth is a planet up to three times the size of Earth and weighing up to 10 times as much. The findings, reported in the Dec. 2 issue of the journal Nature, are a significant milestone toward eventually being able to probe the atmospheres of Earth-like planets for signs of life.The team determined the planet, GJ 1214b, is either blanketed with a
thin layer of water steam or surrounded by a thick layer of high
clouds. If the former, the planet itself would have an icy
composition. If the latter, the planet would be rocky or similar to
the composition of Neptune, though much smaller.
"This is the first super-Earth known to have an atmosphere," said
Jacob Bean, a NASA Sagan Fellow and astronomer at the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "But
even with these new measurements, we can't say yet what that
atmosphere is made of. This world is being very shy and veiling its
true nature from us."
GJ 1214b, first discovered in December 2009, is 2.7 times the size of
Earth and 6.5 times as massive. Previous observations of the planet's
size and mass demonstrated it has a low density for its size, leading
astronomers to conclude the planet is some kind of solid body with an
atmosphere.
The planet orbits close to its dim star, at a distance of 0.014
astronomical units. An astronomical unit is the distance between
Earth and the sun, approximately 93 million miles. GJ 1214b circles
too close to its star to be habitable by any life forms.
Bean and his team observed infrared light as the planet crossed in
front of its star. During such transits, the star's light filters
through the atmosphere. Gases absorb the starlight at particular
wavelengths, leaving behind chemical fingerprints detectable from
Earth. This same type of technique has been used to study the
atmospheres of distant "hot Jupiters," or Jupiter-like planets
orbiting close to their stars, and found gases like hydrogen, methane
and sodium vapor.
In the case of the super-Earth, no chemical fingerprints were
detected; however, this doesn't mean there are no chemicals present.
Instead, this information ruled out some possibilities for GJ 1214b's
atmosphere, and narrowed the scope to either an atmosphere of water
steam or high clouds. Astronomers believe it's more likely the the
atmosphere is too thin around the planet to let enough light filter
through and reveal chemical fingerprints.
"A steamy atmosphere would have to be very dense -- about one-fifth
water vapor by volume -- compared to our Earth, with an atmosphere
that's four-fifths nitrogen and one-fifth oxygen with only a touch of
water vapor," Bean said. "During the next year, we should have some
solid answers about what this planet is truly like."
The team, which included Bean's co-authors - Eliza Miller-Ricci
Kempton, a NASA Sagan Fellow at the University of California in Santa
Cruz, and Derek Homeier of the Institute for Astrophysics in
Gottingen, Germany - examined GJ 1214b using the ground-based Very
Large Telescope at Paranal Observatory in Chile.
"This is an important step forward, narrowing our understanding of the
atmosphere of this planet," said NASA Exoplanet Exploration Program
Scientist Douglas Hudgins. "Bizarre worlds like this make exoplanet
science one of the most compelling areas in astrophysics today."
The Sagan Fellowship Program is administered by the NASA Exoplanet
Science Institute at the California Institute of Technology in
Pasadena. Its purpose is to advance the scientific and technical
goals of NASA's Exoplanet Exploration Program. The program is managed
for NASA by the Jet Propulsion Laboratory in Pasadena, Calif.
For information about NASA's planet-finding missions, visit:
http://planetquest.jpl.nasa.
For information about NASA's Sagan Fellowship Program, visit:
http://nexsci.caltech.edu/
Source: NASA
