A Steamy Super-Earth?


Gliese 1214 and transiting planet
GJ 1214b is small as exoplanets go. But its red-dwarf star is small too, one-fifth the diameter of the Sun, so the planet displays a sizeable profile during its transits. (Artistâ€™s concept.)
Luis Calcada
The star, 14.7-magnitude GJ (Gliese-Jahreiss) 1214 in Ophiuchus, is 300 times dimmer than the Sun with a spectral type of M4.5. Its planet was discovered in 2009 when the MEarth Project detected the planet's silhouette periodically dimming the star. The planet has 6.5 Earth masses, as determined later by the star’s gravitational wobbles, and it circles the little star very closely in just 38 hours. The transits reveal the planet’s diameter to be 2.6 times Earth’s — making its average density very low, only about a third of Earth’s density.

The astronomers detected a telltale absorption spectrum caused by a tiny fraction of the star’s light filtering through the planet’s atmosphere during each transit. The spectrum was featureless, indicating that the upper atmosphere either consists mostly of water vapor or is dominated by high-altitude clouds or haze.

“This is the first super-Earth to have its atmosphere analyzed. We’ve reached a real milestone on the road toward characterizing these worlds,” said team leader Jacob Bean (Harvard–Smithsonian Center for Astrophysics) in a press release.


The measurements clearly show no sign of hydrogen and thus rule out the third option. So the atmosphere is either rich in steam or blanketed by clouds or hazes. The planet’s low density, meanwhile, indicates that it's a waterworld.

“Although we can’t yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,” says Bean. “Followup observations in longer-wavelength infrared light are needed to determine which of these atmospheres exists on GJ 1214b.”

The team's paper appears in the December 2nd issue of Nature.

2 thoughts on “A Steamy Super-Earth?

  1. Roger Halstead

    It seems to me that if the planet is close enough to the sun to make one revolution every 38 hours the solar radiation would be ionizing the water vapor and breaking down the molecules that should then show a Hydrogen signature. But, how cool is the Red Dwarf. Its fusion engine may have stopped, but I’d think a planet orbiting every 38 hours would still receive plenty of radiation.

    Also that close to the sun even though it is a red dwarf and that low a temp would to me indicate a very low, or no CO2 present.

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