Hubble Finds Carbon Dioxide on an Extrasolar Planet

Hubble Finds Carbon Dioxide on an Extrasolar Planet

http://www.nasa.gov/mission_pages/hubble/news/CO2.html

Hi-res image by ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI

NASA's Hubble Space Telescope has discovered carbon dioxide in the
atmosphere of a planet orbiting another star. This breakthrough is an
important step toward finding chemical biotracers of extraterrestrial
life.

The Jupiter-sized planet, called HD 189733b, is too hot for life. But
the Hubble observations are a proof-of-concept demonstration that the
basic chemistry for life can be measured on planets orbiting other
stars. Organic compounds also can be a by-product of life processes and
their detection on an Earthlike planet someday may provide the first
evidence of life beyond our planet.

Previous observations of HD 189733b by Hubble and the Spitzer Space
Telescope found water vapor. Earlier this year, Hubble found methane in
the planet's atmosphere.

"Hubble was conceived primarily for observations of the distant
universe, yet it is opening a new era of astrophysics and comparative
planetary science," said Eric Smith, Hubble Space Telescope program
scientist at NASA Headquarters in Washington. "These atmospheric studies
will begin to determine the compositions and chemical processes
operating on distant worlds orbiting other stars. The future for this
newly opened frontier of science is extremely promising as we expect to
discover many more molecules in exoplanet atmospheres."

Mark Swain, a research scientist at NASA's Jet Propulsion Laboratory in
Pasadena, Calif., used Hubble's near infrared camera and multi-object
spectrometer to study infrared light emitted from the planet, which lies
63 light-years away. Gases in the planet's atmosphere absorb certain
wavelengths of light from the planet's hot glowing interior. Swain
identified carbon dioxide and carbon monoxide. The molecules leave a
unique spectral fingerprint on the radiation from the planet that
reaches Earth. This is the first time a near-infrared emission spectrum
has been obtained for an exoplanet.

"The carbon dioxide is the main reason for the excitement because, under
the right circumstances, it could have a connection to biological
activity as it does on Earth," Swain said. "The very fact we are able to
detect it and estimate its abundance is significant for the long-term
effort of characterizing planets to find out what they are made of and
if they could be a possible host for life."

This type of observation is best done on planets with orbits tilted
edge-on to Earth. They routinely pass in front of and then behind their
parent stars, phenomena known as eclipses. The planet HD 189733b passes
behind its companion star once every 2.2 days. The eclipses allow an
opportunity to subtract the light of the star alone, when the planet is
blocked, from that of the star and planet together prior to eclipse.
That isolates the emission of the planet and makes possible a chemical
analysis of its atmosphere.

"In this way, we are using the eclipse of the planet behind the star to
probe the planet's day side, which contains the hottest portions of its
atmosphere," said team member Guatam Vasisht of NASA's Jet Propulsion
Laboratory. "We are starting to find the molecules and to figure out how
many there are to see the changes between the day side and the night
side."

This successful demonstration of looking at near-infrared light emitted
from a planet is very encouraging for astronomers planning to use NASA's
James Webb Space Telescope after it is launched in 2013. These
biomarkers are best seen at near-infrared wavelengths. Astronomers look
forward to using the James Webb Space Telescope to look
spectroscopically for biomarkers on a terrestrial planet the size of
Earth or a "super-Earth" several times our planet's mass.

"The Webb telescope should be able to make much more sensitive
measurements of these primary and secondary eclipse events," Swain said.

12.09.08