Saturday science subject: Exoplanet atmospheres

Finding out about the atmosphere of planets outside our solar system may have just gotten easier—or at the very least, easier without the need for highly sought observation time on the Hubble and Spitzer space telescopes. As Scientific American reports, most atmosphere-related spectroscopic measurements have been conducted using those telescopes so far. However, an international team of astronomers has managed to detect the atmospheric makeup of a planet 63 light years away using a terrestrial telescope.

In a paper published in the February 4 issue of Nature, a team of researchers from the U.S., England and Germany demonstrates the ability of moderate-size telescopes on the ground to identify the chemical fingerprints in exoplanet atmospheres. (Scientific American is part of Nature Publishing Group.) With observation time on the few active orbiting observatories at a premium, an effective ground-based approach would allow exoplanet characterization to proceed more quickly, and on larger telescopes, to boot.

Mark Swain, an astronomer at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, Calif., and his colleagues used a three-meter telescope in Hawaii to take infrared spectra of the exoplanet HD 189733 b, a relatively nearby exoplanet some 63 light-years distant that was discovered at a French observatory in 2005. HD 189733 b was already known from space-borne observations to harbor several specific molecules in its atmosphere: water, methane, carbon dioxide and carbon monoxide. After painstaking work to cancel out the effects of Earth's atmosphere, Swain and his colleagues found that their ground-based spectra matched up well with those from space where they overlapped. What is more, the observations from the ground turned up a curious feature outside the space-based coverage.

According to Swain, "honing the calibration method" to cancel out the effects of our own planet's atmosphere took a whopping three years. Now, though, Swain tells Scientific American the same technique could be used on other telescopes, which could help us learn more about many of the exoplanets discovered to date—and, who knows, perhaps find Earth's long-lost cousins.

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