Subaru Telescope discovers water vapor atmosphere around super-earth type planet, 40 LY distant

The Subaru Telescope, a ground based 8.2-meter optical-infrared telescope at Mauna Kea has made observations of a “super-earth” planet GJ1214b, orbiting around the star Gliese 1214, a red dwarf star, approximately 40 LY distant.

The telescope has observed how the planet’s atmosphere scatters the light of the parent star during it’s transit across the stellar disc. They infer details about the atmosphere of the planet, based on what is expected for Raleigh scattering for atmospheres of different composition. The Raleigh scattering shown is more characteristic of a dense atmosphere of water vapor than a thick hydrogen atmosphere.

In the solar system, planets can be neatly divided into two categories – terrestrial planets, which are small, dense, and solid with thin atmospheres. They never had the mass needed to retain hydrogen during planetary formation, and so the thick hydrogen atmosphere characteristic of the gas giants was blown off by solar wind, or lost/never-condensed due to thermal motion early in their history. The gas giants had enough mass relative to their position to retain hydrogen, and built up extremely deep hydrogen atmospheres. The gas giants are large, less dense overall, and mostly light gas.

Observations of exoplanets though show that there are many planets with masses and diameters in between those of Earth, the largest terrestrial planet of the Solar System, and the smallest gas giants, (the ice giants of the outer solar system). It is unknown what these planets are like – whether they are more like terrestrial planets, or like very small gas-giants. Other than diameter and orbit characteristics, it is hard to know anything about the exo-planets directly with our current detection methods.

Gliese 1214 b is one such super-Earth, with 2.4 times the radius, and an estimated 6.5 times the mass of our planet. Depending on how much light is reflected, it could have equilibrium temperatures between 120 and 282 C. While this planet is probably too hot for Earth-life, it is not so hot that it is impossible that some form of molecular biology could exist. Hydrothermal vent creatures have been known to live in up to 80 C.

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