For the first time, carbon dioxide has been detected in the atmosphere of an exoplanet, astronomers working with the Hubble Space Telescope report. Although the Jupiter-sized planet, which closely orbits the star HD 189733 about 63 light-years from Earth, is much too hot to support life, scientists are hailing the discovery as an exciting technical achievement. “In that context, the carbon dioxide measurement constitutes a dress rehearsal …for our long-term goal of trying to detect signs of life or signs of habitability on terrestrial-mass planets or super Earths in the habitable zone,” [Science News] says Mark Swain of NASA’s Jet Propulsion Laboratory.
Researchers deduced the presence of carbon dioxide by measuring the planet’s light spectrum with the Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS). To isolate the light spectrum coming from the planet, researchers used a method known as “secondary transit.” This involves recording the light spectrum of the planet and its star, and then measuring the spectrum of the star alone while the planet is hidden behind it. The difference of the two spectra is the spectrum of the light coming directly from the planet [Nature News]. Unlike previous measurements that focused on the mid-infrared range, NICMOS took measurements in the near-infrared range, enabling detection of the carbon dioxide signature.
It’s unclear how the carbon dioxide formed on the planet. Swain points to the proximity of the planet to its star and suggests that the intense ultraviolet radiation may have caused a chemical reactions in the planet’s atmosphere. Similar reactions are thought to have played a role in the formation of Earth’s early atmosphere. The researchers also confirmed the presence of water vapor and carbon monoxide in the planet’s atmosphere. Their findings will be published in Astrophysical Journal Letters.
With the latest discovery, “three of the Big Four biomarkers for habitable/inhabited worlds have now been seen: water, methane, and now carbon dioxide,” though not all on the same exoplanet, says planet-formation theorist Alan Boss. “The only one that has not yet been detected is oxygen/ozone.” [Space.com].
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