Alien SUPER-EARTH: If there is LIFE up there, it'll be moaning about the weather

'The first ten million years were the worst,' said Marvin

Artist's impression of a cloudy exoplanet

Two of the most common type of planets found in the Milky Way galaxy are cloudy, damp super-worlds, according to data from NASA's Hubble Space Telescope.

Artist's impression of a cloudy exoplanet

Boffins have been trying for some time to figure discern what sort of atmospheres surround two planets: GJ 436b, which is 36 light years from Earth in the constellation Leo, and GJ 1214b, which is 40 light years away in Ophiuchus. Developing ways to assess the atmospheres of alien worlds will eventually help scientists to find potentially habitable planets beyond our solar system.

These two exoplanets are midway in size between rocky planets like Earth and gas giants like Jupiter. GJ 436b has been known as a warm Neptune, because it's closer to its star than our own icy Neptune is to the Sun. GJ 1214b is classed as a super-Earth because of its size.

Hubble captured images of 436b in transit around its parent star and found that the world was featureless with no chemical fingerprints whatsoever.

"Either this planet has a high cloud layer obscuring the view, or it has a cloud-free atmosphere that is deficient in hydrogen, which would make it very unlike Neptune," said Caltech's Heather Knutson, author of the paper on 436b.

"Instead of hydrogen, it could have relatively large amounts of heavier molecules such as water vapour, carbon monoxide, and carbon dioxide, which would compress the atmosphere and make it hard for us to detect any chemical signatures."

Similar observations formed the basis of the paper on 1214b, when Hubble also found no chemical fingerprint in the atmosphere. But in that planet's case, the data was so precise that boffins could rule out cloud-free compositions of water vapour, methane, nitrogen, carbon monoxide and carbon dioxide for the first time.

"Both planets are telling us something about the diversity of planet types that occur outside of our own solar system; in this case we are discovering we may not know them as well as we thought," said Knutson. "We'd really like to determine the size at which these planets transition from looking like mini-gas giants to something more like a water world or a rocky, scaled-up version of the Earth. Both of these observations are fundamentally trying to answer that question."

The studies were published in two separate papers in this month's Nature: "A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b" and "Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b". ®

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