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Super-Earth's atmosphere analyzed for first time

The first-ever analysis of the atmosphere of an alien planet classified as a so-called "super-Earth" has revealed a distant world that is likely covered with either water vapor or a thick haze, scientists announced Wednesday.
Image: Super-Earth
An artist's conception shows a super-Earth known as GJ 1214b with its parent star and another world. Researchers have analyzed the atmosphere of GJ 1214b, which is about 40 light-years from Earth.David A. Aguilar / CfA
/ Source: Space.com

The first-ever analysis of the atmosphere of an alien planet classified as a so-called "super-Earth" has revealed a distant world that is likely covered with either water vapor or a thick haze, scientists announced Wednesday.

The exoplanet GJ 1214b, which orbits a star 40 light-years from Earth, offers astronomers a unique chance to study its atmosphere because it passes directly in front of its parent star from Earth's line of sight. That means that once an orbit, the star's light is filtered as it passes through the planet's atmosphere on its way to Earth, taking with it an imprint from the chemicals there. [Illustration of alien planet GJ 1214b]

"We're trying to get at, what's the main component of this planet's atmosphere?" said lead researcher Jacob Bean, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

GJ 1214b is called a super-Earth because it is larger than our home planet, but still smaller than gas giants like Jupiter and Saturn. It was first discovered in 2009 and has been studied ever since.

A watery super-Earth?
In a comparison with our solar system's inhabitants, GJ 1214b most closely resembles Neptune, Bean said. The alien planet has a radius 2.5 times the size of Earth's and is about 6.5 times the mass of our planet, researchers said.

Astronomers have discovered more than 500 alien planets beyond our solar system so far, with hundreds more expected to be confirmed in upcoming months.

Bean and his colleagues observed the GJ 1214b system with the FORS instrument on the European Southern Observatory's Very Large Telescope in Chile. The instrument analyzes the spectrum of light from a target to determine the object's composition. Rather than find a signal crawling with interesting elements, the scientists actually discovered that GJ 1214b's atmosphere bears a relatively flat, featureless signature.

"That might seem a bit boring, but that's actually a very powerful constraint," Bean told Space.com.

It means, for example, that the exoplanet's atmosphere can't contain much hydrogen, which typically leaves a strong feature in the spectrum of light coming from a planet.

The astronomers concluded that the alien world's atmosphere is most likely dominated by a puffy atmosphere or water vapor — or it may be blanketed by a haze of clouds that are blocking other chemicals underneath.

"This isn't a definitive result, but it's very exciting," Bean said. "It points the way toward the future."

Gazing below alien planet's cloud
The scientists hope to follow up with more detailed observations, particularly in the infrared range of light that may be able to penetrate the possible cloud cover. [Gallery: Strangest Alien Planets]

Although water vapor may sound promising for extraterrestrial life, which scientists think will require water to survive, scientists said GJ 1214b is not a candidate for hosting life.

"This planet has basically no potentiality for habitability, whether it has a puffy atmosphere or a cloud atmosphere," Bean said. That's because it's probably way too warm for liquid water to exist in large quantities, which is thought to be the key for life.

Because super-Earth planets are easier to detect than relatively small, dim Earthlike planets, yet more difficult to find than bright large gas giants, they represent the cutting edge of astronomers' ability to study planets beyond the solar system.

"Super-Earths are really at the frontier of exoplanet research right now," Bean said. "We've gotten to the point where we can finally discover and characterize these planets. I think over the next few years there's really going to be an explosion of work done in this area."

The results of the study are detailed in Thursday's issue of the journal Nature.