NASA'S Spitzer Finds Evidence for an Exoplanet Smaller than Earth

July 18, 2012

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

RELEASE: 12-238

NASA'S SPITZER FINDS EVIDENCE FOR AN EXOPLANET SMALLER THAN EARTH

WASHINGTON -- Astronomers using NASA's Spitzer Space Telescope have
detected what they believe is a planet two-thirds the size of Earth.
The exoplanet candidate, called UCF-1.01, is located a mere 33
light-years away, making it possibly the nearest world to our solar
system that is smaller than our home planet.

Exoplanets circle stars beyond our sun. Only a handful smaller than
Earth have been found so far. Spitzer has performed transit studies
on known exoplanets, but UCF-1.01 is the first ever identified with
the telescope, pointing to a possible role for Spitzer in helping
discover potentially habitable, terrestrial-sized worlds.

"We have found strong evidence for a very small, very hot and very
near planet with the help of the Spitzer Space Telescope," said Kevin
Stevenson from the University of Central Florida in Orlando.
Stevenson is lead author of the paper, which has been accepted for
publication in The Astrophysical Journal. "Identifying nearby small
planets such as UCF-1.01 may one day lead to their characterization
using future instruments."

The hot new planet candidate was found unexpectedly in Spitzer
observations. Stevenson and his colleagues were studying the
Neptune-sized exoplanet GJ 436b, already known to exist around the
red-dwarf star GJ 436. In the Spitzer data, the astronomers noticed
slight dips in the amount of infrared light streaming from the star,
separate from the dips caused by GJ 436b. A review of Spitzer
archival data showed the dips were periodic, suggesting a second
planet might be blocking out a small fraction of the star's light.

This technique, used by a number of observatories including NASA's
Kepler space telescope, relies on transits to detect exoplanets. The
duration of a transit and the small decrease in the amount of light
registered reveals basic properties of an exoplanet, such as its size
and distance from its star. In UCF-1.01's case, its diameter would be
approximately 5,200 miles (8,400 kilometers), or two-thirds that of
Earth. UCF-1.01 would revolve quite tightly around GJ 436, at about
seven times the distance of the Earth from the moon, with its "year"
lasting only 1.4 Earth days. Given this proximity to its star, far
closer than the planet Mercury is to our sun, the exoplanet's surface
temperature would be more than 1,000 degrees Fahrenheit (almost 600
degrees Celsius).

If the roasted, diminutive planet candidate ever had an atmosphere, it
almost surely has evaporated. UCF-1.01 might therefore resemble a
cratered, mostly geologically dead world like Mercury. Paper
co-author Joseph Harrington, also of the University of Central
Florida and principal investigator of the research, suggested another
possibility; that the extreme heat of orbiting so close to GJ 436 has
melted the exoplanet's surface.

"The planet could even be covered in magma," Harrington said.

In addition to UCF-1.01, Stevenson and his colleagues noticed hints of
a third planet, dubbed UCF-1.02, orbiting GJ 436. Spitzer has
observed evidence of the two new planets several times each. However,
even the most sensitive instruments are unable to measure exoplanet
masses as small as UCF-1.01 and UCF-1.02, which are perhaps only
one-third the mass of the Earth. Because knowing the mass is required
for confirming a discovery, the paper authors are cautiously calling
both bodies exoplanet candidates for now.

Of the approximately 1,800 stars identified by Kepler as candidates
for having planetary systems, just three are verified to contain
sub-Earth-sized exoplanets. Of these, only one exoplanet is thought
to be smaller than the Spitzer candidates, with a radius similar to
Mars, or 57 percent that of Earth.

"I hope future observations will confirm these exciting results, which
show Spitzer may be able to discover exoplanets as small as Mars,"
said Michael Werner, Spitzer Project Scientist at NASA's Jet
Propulsion Laboratory (JPL) in Pasadena, Calif. "Even after almost
nine years in space, Spitzer's observations continue to take us in
new and important scientific directions."

JPL manages Spitzer for NASA's Science Mission Directorate in
Washington. Science operations are conducted at the Spitzer Science
Center at Caltech in Pasadena. Caltech manages JPL for NASA.

For more information about Spitzer, visit:

http://www.nasa.gov/spitzer


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