Hubble Spots Cloudy Atmospheres on Two Nearby Exoplanets

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On the eve of a new year, astronomers have just revealed that two nearby exoplanets are covered in an atmosphere thick with clouds.

Two new papers, both to be published in the journal Nature, examine the planets GJ 436b and GJ 1214b. GJ 436b is located just 36 light-years from our solar system and is thought to be a "warm Neptune" - a gas giant similar to our outer-most planet, but much closer to its sun. GJ 1214b is just 40 light-years away and is dubbed a "super-Earth" for its size and position relative to its star.

Researchers used NASA's Hubble Space Telescope to observe these planets as they passed in front of their respective suns. Instead of the revealing chemical spectra that astronomers would normally find as starlight filters through the atmosphere of planets, the studies' authors instead found spectra with no chemical markers.

"Either this planet [GJ 436b] 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 Heather Knutson, lead on the GJ436b observations and an astronomer at the California Institute of Technology. "Instead of hydrogen, it could have relatively large amounts of heavier molecules such as water vapor, carbon monoxide, and carbon dioxide, which would compress the atmosphere and make it hard for us to detect any chemical signatures."

Follow-up observations of GJ 1214b found evidence that it too had a thick layer of clouds on top of an atmosphere made up of mainly of water vapor or hydrogen. The GJ1214b observations have also ruled out the possibility that the planet's atmosphere cloudless but dominated by common chemicals such as water vapor, nitrogen, or carbon dioxide.

"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."

Image via NASA/ESA/L. Kreidberg and J. Bean (University of Chicago)/H. Knutson (California Institute of Technology)

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