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In an encouraging find for habitability researchers, astronomers have detected molecules on the smallest exoplanet ever 鈥� a Neptune-sized planet about 120 light-years from Earth. The team behind the discovery says this means the dream of understanding the atmospheres on planets even closer to size of Earth is getting closer.

鈥淭he work we are doing now is important for future studies of super-Earths and even smaller planets, because we want to be able to pick out in advance the planets with clear atmospheres that will let us detect molecules,鈥� stated co-author Heather Knutson, of the California Institute of Technology.

This particular world is not life-friendly as we understand it, however. Called HAT-P-11b, it鈥檚 not only a gas giant but also a planet that orbits extremely close to its star 鈥� making one circle every five days. And unusually among planets of its size that were previously probed by astronomers, it appears to have clear skies.

The team examined the world using the Hubble Space Telescope鈥檚 Wide Field Camera 3, looking at the planet as it passed across the face of its star. The team compared the signature of elements observed when the planet was in front of the star and when it was not, and discovered telltale signs of water vapor in its atmosphere.

While other planets outside our solar system are known to have water vapor, the ones previously examined are much larger. Jupiter-sized planets are much easier to examine not only because they are larger, but their atmospheres puff up more (making them more visible from Earth.)

To confirm the water vapor was not a false signal from sunspots on the parent star (which also can contain it), the team used the Kepler and Spitzer space telescopes to confirm the information. (Kepler鈥檚 single field of view around the constellation Cygnus, which it had been peering at for about four years, happily included the zone where HAT-P-11b was orbiting.) The infrared information from Spitzer and the visible-light data from Kepler both showed the sunspots were too hot for water vapor.

Further, the discovery shows there were no clouds in the way of the observations 鈥� a first for planets of that size. The team also hopes that super-Earths could have clear skies, allowing astronomers to analyze their atmospheres.

鈥淲hen astronomers go observing at night with telescopes, they say 鈥榗lear skies鈥� to mean good luck,鈥� stated lead author Jonathan Fraine, of the University of Maryland, College Park. 鈥淚n this case, we found clear skies on a distant planet. That鈥檚 lucky for us because it means clouds didn鈥檛 block our view of water molecules.鈥�

The research was聽published in the journal Nature.

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About聽Elizabeth Howell

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter@howellspace聽or contact her at聽her website.