US researchers have definitively characterized the atmosphere of a super-Earth class planet outside our solar system for the first time.

It might seem easy and perhaps boring. Today's forecast: cloudy. Tomorrow: overcast. Extended outlook: more clouds. And temperatures are likely to stay around 232 degrees Celsius, since the planet orbits very close to its parent star.

The scrutinized planet, GJ 1214b, is classified as a super- Earth type planet because its mass is intermediate between those of Earth and Neptune.

Previous studies of GJ 1214b yielded two possible interpretations of the planet's atmosphere. Its atmosphere could consist entirely of water vapor or some other type of heavy molecule, or it could contain high-altitude clouds that prevent the observation of what lies underneath.

But now a team of astronomers led by Laura Kreidberg and Jacob Bean of the University of Chicago said Tuesday they have detected clear evidence of clouds in the atmosphere of GJ 1214b from data collected with the Hubble Space Telescope. The Hubble observations used 96 hours of telescope time spread over 11 months.

"I think it's very exciting that we can use a telescope like Hubble that was never designed with this in mind, do these kinds of observations with such exquisite precision, and really nail down some property of a small planet orbiting a distant star," said Bean, an assistant professor and the project's principal investigator.

Kreidberg, a third-year graduate student and first author of the new paper, believed their research "lays the foundation for characterizing other Earths with similar techniques."

GJ 1214b, discovered in 2009, is located just 40 light years from Earth, in the direction of the constellation Ophiuchus. Because of its proximity to our solar system and the small size of its host star, GJ 1214b is the most easily observed super-Earth. It transits, or passes in front of its parent star, every 38 hours, giving scientists an opportunity to study its atmosphere as starlight filters through it.

Kreidberg, Bean and their colleagues used Hubble to precisely measure the spectrum of GJ 1214b in near-infrared light, finding what they consider definitive evidence of high clouds blanketing the planet. These clouds hide any information about the composition and behavior of the lower atmosphere and surface, they said.

The clouds' composition is unknown but computer simulations predict that they could be made out of potassium chloride or zinc sulfide. "You would expect very different kinds of clouds to form than you would expect, say, on Earth," Kreidberg said.

The results were published in the British journal Nature.