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An exoplanet
with some fizz
co detection bolsters
²
search for signs of life
By Ron Cowen
Moving one step closer to finding distant
fingerprints of life, astronomers have for
the first time detected carbon dioxide in
the atmosphere of a planet that orbits a
star other than the sun.
The extrasolar planet and its star lie
about 63 light-years from Earth. Slightly
bigger than Jupiter, the gaseous body
circles its parent star at a proximity
that renders it far too hot to support
life. But the finding bodes well for ultimately detecting carbon dioxide and
other potential markers of life on planets that lie far enough from their parent
stars to be habitable, says Mark Swain
of NASA’s Jet Propulsion Laboratory in
Pasadena, Calif.
In the atmospheres of more temperate planets, carbon dioxide — along with
water, methane and oxygen— can be
made by biological processes. “In that
context,” Swain says, “the carbon dioxide measurement constitutes a dress
An artist’s impression shows an extrasolar planet diving behind its parent star.
rehearsal … for our long-term goal of
trying to detect signs of life or signs of
habitability on terrestrial-mass planets
or superEarths in the habitable zone”
around a star, which is where water could
exist as a liquid.
Using the Hubble Space Telescope’s
Near Infrared Camera and Multi-Object Spectrometer, Swain and his colleagues recorded infrared spectra from
the planet, which periodically crosses
in front of its parent star as seen from
Earth. When the hot planet lies side by
side with its parent star, HD 189733,
astronomers can detect the spectra of
infrared radiation, or heat, from both
star and planet. When the planet dives
behind the star, only the infrared radia-
tion from the star reaches Earth. Subtracting the two measurements provides
the amount of infrared radiation given
off by the planet alone.
The spectra of the planet’s radiation,
recorded by the Hubble instrument,
reveal chemical constituents of the
planet’s atmosphere. The team found
evidence of water vapor, which was previously detected in the planet’s atmosphere, as well as carbon monoxide and
the never-before-seen carbon dioxide, the
researchers report in an upcoming Astrophysical Journal Letters. Team member
Gautam Vasisht of JPL also presented the
findings on November 19 in Paris at the
Molecules in the Atmospheres of Extrasolar Planets meeting.
Stairways to climate stability
they may not be the steps to paradise, but several outcrops of martian
rocks (shown at left) do resemble stairs, displaying a pattern that suggests the ancient climate on the red planet wasn’t always an amalgam
of cataclysmic floods, volcanic eruptions and crater-gouging impacts.
Instead, the evenly spaced, eons-old sedimentary rock layers in the
Arabia terra region imply that during a brief time several billion years
ago, the climate varied in a gentler, more predictable fashion—changes
that may have been tied to variations in the planet’s tilt. Evidence indicates that mars’ spin axis has wobbled significantly in the last several
million years, periodically cooling the equatorial region and warming
the poles as they received more sunlight. the new findings hint that
the axis may have had a similar wobble in the much more distant past,
notes Kevin lewis of caltech. lewis and his colleagues describe those
findings, based on images taken by the mars reconnaissance orbiter’s
HirISE camera, in the Dec. 5 Science. —Ron Cowen
From top: ESA, NASA, m. KorNmESSEr (ESA/HubblE), StScI;
topogrApHy: cAltEcH, HIrISE ImAgES: u oF ArIzoNA, Jpl/NASA
