Volcanic activity detected on distant planet

Astronomers have for the first time observed changing conditions on a solid planet far beyond our solar system. The planet, 55 Cancri-e, is a volcanic inferno on which Cambridge university researchers have detected temperatures swinging from 1,000C to 2,700C.

The study, published in Monthly Notices of the Royal Astronomical Society, is a landmark in the investigation of planets elsewhere in the galaxy. In the 20 years since these so-called exoplanets were first detected, astronomers have found almost 2,000 of them orbiting distant stars. But only now is technology reaching the stage when scientists can begin to deduce their environmental conditions.

55 Cancri-e is a "super-Earth", a rocky rather than gaseous planet with a diameter about twice that of Earth. It is one of five planets around a sun-like star in the Cancer constellation about 40 light-years or 380 trillion km away from us. Unlike Earth it orbits very close to its star, so a year on 55 Cancri-e lasts just 18 hours - and rather than rotating it is "tidally locked" with a torrid day side constantly exposed to the stellar heat.

Analysing observations of 55 Cancri-e taken over two years by Nasa's Spitzer space telescope, the Cambridge researchers have discovered huge swings in temperature on the hot side, which they interpret as resulting from extensive volcanic activity on a huge scale. Volcanoes may eject gigantic plumes of gas and dust that occasionally blanket the partially molten surface and cool it.

"This is the first time we've seen such drastic changes in light emitted from an exoplanet," said Nikku Madhusudhan of Cambridge's Institute of Astronomy. "No signature of thermal emissions or surface activity has ever been detected for any other super-Earth to date."

Much early research on exoplanets has focused on gas giants such as Jupiter and Saturn, because their huge size makes them easier to observe. Mapping atmospheric conditions on smaller rocky planets has been much harder.

Scientists have been refining their theories about 55 Cancri-e since it was first detected in 2004. Earlier observations suggested that it was very rich in carbon - and might even be made of diamond. The latest analysis has undermined this idea.

"The present observations open a new chapter in our ability to study the conditions on rocky exoplanets using current and upcoming large telescopes," Mr Madhusudhan said.

Astronomers hope to use a new generation of land-based and space telescopes to observe exoplanets similar to Earth in their size, environment and chemical composition, which could provide suitable habitats for life to originate and evolve.

Direct observation of their surface features is still a distant dream but biological processes may be detected more quickly through their effect on the planetary atmosphere.

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