Carbon Dioxide…in Space?

Carbon dioxide has been discovered by the Hubble Space Telescope in the atmosphere of a planet orbiting another star. The discovery, which was recently announced by NASA is, according to the agency, an important step towards finding chemical biotracers of extraterrestrial life. While the planet in question is the size of Jupiter and is too hot to contain life, scientists say the Hubble observations leave no room for doubt, as they are a “proof-of-concept demonstration that the basic chemistry for life can be measured on planets orbiting other stars.”

The latest discovery wasn’t the first to reveal “Earthlike” features of the planet, which was given the official name “HD 189733b.” Previous observations by both the Hubble and Spitzer Space Telescopes already revealed both methane and water vapor in the planet’s atmosphere (as was previously reported by TFOT in August 2007). According to the scientists, the latest discovery provides strong motivation for continued search for organic compounds on the planet – such substances can be a by-product of life processes and if found will be the first evidence of life beyond our planet.

”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.”

Researchers were observing the infrared light emitted from the planet using Hubble’s near-infrared camera and multi-object spectrometer when they noticed something unusual. The gases in the planet’s atmosphere, which normally absorb certain wavelengths of light from the planet’s hot glowing interior, showed traces of both carbon dioxide and carbon monoxide. In their first attempt to obtain a near-infrared emission spectrum of an exoplanet, the scientists identified the compounds by discovering their molecules’ unique spectral fingerprints, left on the planet’s radiation reaching Earth. “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,” said Mark Swain, a research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “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.”

The scientists say that HD 189733b possesses a unique characteristic, without which the necessary chemical analysis would have been a lot more difficult to perform – the planet frequently orbits its parent star, passing in front of and behind it once every few days. Moreover, since HD 189733b’s orbit is tilted edge-on to Earth, each time the planet passes behind its star, it is completely hidden from sight and all emission from it is blocked. Such so-called “eclipses” allowed scientists to accurately calculate the light emitting from the star alone, what in turn helped them to isolate the planet’s emission from the total incoming infrared light. “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.”

Astronomers are more than encouraged by the latest observations, especially in light of the planned launch of NASA’s James Webb Space Telescope in 2013. The new telescope, they say, will “be able 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 added.

TFOT has previously covered many cosmological and space related discoveries, including the most luminous X-ray cluster ever to be detected at a distance of nearly 8 billion light years away from Earth and the dustiest binary star system, recently discovered by a team of astronomers from UCLA and Caltech.

More information on the HD 189733b carbon dioxide discovery can be found on NASA’s website.

Icon image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA

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