Super-Earth may have water as steam or high clouds in atmosphere

On the heels of the discovery of the 500th exoplanet, an international team of astronomers has analyzed the atmosphere of a super-Earth exoplanet and found that the atmosphere is either mostly water in the form of steam or is dominated by thick clouds or hazes.

This is a world 40 light-years away and more than 6 times as massive than our own Earth.

The team used ESO’s Very Large Telescope to study the planet – called GJ 1214b – as it passed in front of its parent star and some of the starlight passed through the planet’s atmosphere.

“We’ve reached a real milestone on the road toward characterizing these worlds,” said Jacob Bean of the Harvard–Smithsonian Center for Astrophysics, who led the discovery team.

The host star of GJ 1214b lies in the direction of the constellation of Ophiuchus the Serpent Bearer. Though it is more massive and also larger than Earth, this planet orbits some 70 times closer than our Earth to our sun. Thus its “year” goes faster – much faster. It completes an orbit and travels across the disk of its star once every 38 hours.

Before the new observations, astronomers had suggested three possible atmospheres for GJ 1214b. The first was a water atmosphere – which, given the close proximity of GJ 1214b to its star, would be in the form of steam. The second possibility was that this is a rocky world with an atmosphere consisting mostly of hydrogen, but with high clouds or hazes obscuring the view. The third option was that this exoplanet was like a mini-Neptune, with a small rocky core and a deep hydrogen-rich atmosphere.

The new measurements do not show the telltale signs of hydrogen and hence rule out the third option. Therefore, the atmosphere is either rich in steam, or it is blanketed by clouds or hazes, similar to those seen in the atmospheres of Venus and Titan in our solar system.

“Although we can’t yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,” says Bean. “Follow-up observations in longer wavelength infrared light are now needed to determine which of these atmospheres exists on GJ 1214b.”

Source: ESO. First Super-Earth Atmosphere Analyzed

December 1, 2010

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