NASA's Spitzer Reveals First
Carbon-Rich Planet







This artist's concept
shows the searing-hot gas planet WASP-12b (orange orb) and its star.
NASA's Spitzer Space Telescope discovered that the planet has more
carbon than oxygen, making it the first carbon-rich planet ever
observed. Image credit: NASA/JPL-Caltech
›
Full image and caption












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December 08, 2010


PASADENA, Calif. -- Astronomers have discovered that a huge, searing-hot
planet orbiting another star is loaded with an unusual amount of
carbon. The planet, a gas giant named WASP-12b, is the first carbon-rich
world ever observed. The discovery was made using NASA's Spitzer Space
Telescope, along with previously published ground-based observations.

"This planet reveals the astounding diversity of worlds out there,"
said Nikku Madhusudhan of the Massachusetts Institute of Technology,
Cambridge, lead author of a report in the Dec. 9 issue of the journal
Nature. "Carbon-rich planets would be exotic in every way -- formation,
interiors and atmospheres."

It's possible that WASP-12b might harbor graphite, diamond, or even a
more exotic form of carbon in its interior, beneath its gaseous layers.
Astronomers don't currently have the technology to observe the cores of
exoplanets, or planets orbiting stars beyond our sun, but their
theories hint at these intriguing possibilities.

The research also supports theories that carbon-rich rocky planets
much less massive than WASP-12b could exist around other stars. Our
Earth has rocks like quartz and feldspar, which are made of silicon and
oxygen plus other elements. A carbon-rich rocky planet could be a very
different place.

"A carbon-dominated terrestrial world could have lots of pure carbon
rocks, like diamond or graphite, as well as carbon compounds like tar,"
said Joseph Harrington of the University of Central Florida, in
Orlando, who is the principal investigator of the research.

Carbon is a common component of planetary systems and a key
ingredient of life on Earth. Astronomers often measure carbon-to-oxygen
ratios to get an idea of a star's chemistry. Our sun has a
carbon-to-oxygen ratio of about one to two, which means it has about
half as much carbon as oxygen. None of the planets in our solar system
is known to have more carbon than oxygen, or a ratio of one or greater.
However, this ratio is unknown for Jupiter, Saturn, Uranus, and Neptune.
Unlike WASP-12b, these planets harbor water -- the main oxygen carrier
-- deep inside their atmospheres, making it hard to detect.


WASP-12b is the first planet ever to have its carbon-to-oxygen ratio
measured at greater than one (the actual ratio is most likely between
one and two). This means the planet has excess carbon, some of which is
in the form of atmospheric methane.

"When the relative amount of carbon gets that high, it's as though you
flip a switch, and everything changes," said Marc Kuchner, an
astronomer at NASA Goddard Space Flight Center, Greenbelt, Md., who
helped develop the theory of carbon-rich rocky planets but is not
associated with the study. "If something like this had happened on
Earth, your expensive engagement ring would be made of glass, which
would be rare, and the mountains would all be made of diamonds."

Madhusudhan, Harrington and colleagues used Spitzer to observe
WASP-12b as it slipped behind its star, in a technique known as
secondary eclipse, which was pioneered for exoplanets by Spitzer. These
data were combined with previously published observations taken from the
ground with the Canada-France-Hawaii Telescope at Mauna Kea, Hawaii.
Madhusudhan used the data to conduct a detailed atmospheric analysis,
revealing chemicals such as methane and carbon monoxide in the planet's
atmosphere.

WASP-12b derives its name from the consortium that found it, the
Wide Angle Search for Planets. It is 1.4 times as massive as Jupiter and
located roughly 1,200 light-years away from Earth. This blistering
world whips around its star in a little over a day, with one side always
facing the star. It is so close to its star that the star's gravity
stretches the planet into an egg-like shape. What's more, the star's
gravity is siphoning mass off the planet into a thin disk that orbits
around with it.

The Spitzer data also reveal more information about WASP-12b's
temperature. The world was already known to be one of the hottest
exoplanets found so far; the new observations indicate that the side
that faces the star is 2,600 Kelvin, or 4,200 degrees Fahrenheit. That's
more than hot enough to melt steel.

Other authors of the paper are Kevin Stevenson, Sarah Nymeyer,
Christopher Campo, Jasmina Blecic, Ryan Hardy, Nate Lust, Christopher
Britt and William Bowman of University of Central Florida, Orlando;
Peter Wheatley of the University of Warwick, United Kingdom; Drake
Deming of NASA Goddard Space Flight Center, Greenbelt, Md.; David
Anderson, Coel Hellier and Pierre Maxted of Keele University, United
Kingdom; Andrew Collier-Cameron of the University of St. Andrews, United
Kingdom; Leslie Hebb of Vanderbilt University, Nashville, Tenn.; Don
Pollacco of Queen's University, United Kingdom; and Richard West of the
University of Leicester, United Kingdom.

The Spitzer observations were made before it ran out of its liquid
coolant in May 2009 and began its warm mission. NASA's Jet Propulsion
Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA's
Science Mission Directorate, Washington. Science operations are
conducted at the Spitzer Science Center at the California Institute of
Technology, also in Pasadena. Caltech manages JPL for NASA. For more
information about Spitzer, visit http://spitzer.caltech.edu/
and http://www.nasa.gov/spitzer
. More information about NASA’s search for exoplanets is at: http://planetquest.jpl.nasa.gov/
.