The Hubble space telescope has discovered carbon dioxide in the air of a planet orbiting a distant star. Astronomers are excited because it confirms they have the power to detect signs of life in alien solar systems.

The gas was revealed in the atmosphere of a planet the size of Jupiter labelled HD 189733b in the constellation of Vulpecula the Fox.

It is too hot for life as we know it to exist there. But it offers the prospect that organic chemicals could be measured on more friendly worlds.

Scientists have already detected water vapour and methane in the atmosphere of the planet which lies 63 light-years away from Earth. They have even observed its sunsets.

Mark Swain of NASA’s Jet Propulsion Laboratory in California, said last night: “This is exciting because Hubble is allowing us to see molecules that probe the conditions, chemistry, and composition of atmospheres on other planets.

“Thanks to Hubble we’re entering an era where we are rapidly going to expand the number of molecules we know about on other planets.”

He added: “The carbon dioxide is kind of the main focus of the excitement, because that is a molecule that under the right circumstances could have a connection to biological activity as it does on Earth.

“The very fact that we’re able to detect it, and estimate its abundance, is significant for the long-term effort of characterizing planets both to find out what they’re made of and to find out if they could be a possible host for life.”

An international team of astronomers used Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to study infrared light from the planet as it was eclipsed by its parent star. They identified not only carbon dioxide, but also carbon monoxide.

The molecules leave their own 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 extrasolar planet.

One of the researchers, Giovanna Tinetti, of University College London, said: “In the terrestrial planets of our Solar System, carbon dioxide plays a crucial role for the stability of climate.

“On Earth, carbon dioxide is one of the ingredients of the photosynthesis and a key element for the carbon cycle. Our observations represent a great opportunity to understand the role of carbon dioxide in the atmospheres of hot Jupiter-type planets.”

Picture: An artist’s impression of HD 189733b being eclipsed by its parent star. (Credit: ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI).

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