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 smaller than gas giants like Jupiter and Saturn. It was first discovered in 2009 and has been studied ever since.
A watery super-Earth?
Among our solar system's inhabitants, Neptune is the planet that most closely resembles GJ 1214b, Bean said. The alien planet has a radius 2.5 times the size of Earth's and has about 6.5 times the mass, 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 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 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 water vapor or blanketed by a haze of clouds that is 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 might be able to penetrate the possible cloud cover. [Gallery: Strangest Alien Planets]
Although the prospect of water vapor may sound promising in the search for extraterrestrial life, scientists said GJ 1214b is not a candidate for hosting life. That's because the planet is probably way too warm for liquid water to exist in large quantities.
"This planet has basically no potentiality for habitability, whether it has a puffy atmosphere or a cloud atmosphere," Bean said.
Super-Earths are easier to detect than a relatively small, dim Earth-like planet would be, yet are more difficult to find than bright, large gas giants, so they represent the cutting edge in 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 tomorrow's (Dec. 2) issue of the journal Nature.
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