Super-Earth may have water-rich atmosphere

Artist's rendition of a transit of GJ 1214 b in blue light. The blue sphere represents the host star GJ 1214, and the black ball in front of it on the right is GJ 1214 b

Blue light observations of a super-Earth - 40 light years from our planet - have indicated that it may have a water-rich atmosphere, astronomers say.

Blue light observations of a super-Earth - 40 light years from our planet - have indicated that it may have a water-rich atmosphere, astronomers say. 

Japanese astronomers and planetary scientists used Subaru Telescope's two optical cameras, Suprime-Cam and the Faint Object Camera and Spectrograph (FOCAS), with a blue transmission filter to observe planetary transits of super-Earth GJ 1214 b (Gilese 1214 b).

The team investigated whether this planet has an atmosphere rich in water or hydrogen.

The Subaru observations show that the sky of this planet does not show a strong Rayleigh scattering feature, which a cloudless hydrogen-dominated atmosphere would predict. When combined with the findings of previous observations in other colours, this new observational result implies that GJ 1214 b is likely to have a water-rich atmosphere.

Super-Earths are emerging as a new type of exoplanet with a mass and radius larger than the Earth's but less than those of ice giants in our Solar System, such as Uranus or Neptune.

Scientists focused their efforts on investigating the atmospheric features of a well-known super-Earth, GJ 1214 b, located 40 light years from Earth in the constellation Ophiuchus, northwest of the center of our Milky Way galaxy.

The team's research examined features of light scattering of GJ 1214 b's transit around its star. Current theory posits that a planet develops in a disk of dense gas surrounding a newly formed star.

The element hydrogen is a major component of a protoplanetary disk, and water ice is abundant in an outer region beyond a so-called "snow line."

Findings about where super-Earths have formed and how they have migrated to their current orbits point to the prediction that hydrogen or water vapour is a major atmospheric component of a super-Earth, researchers said.

Planetary transits enable scientists to investigate changes in the wavelength in the brightness of the star (ie, transit depth), which indicate the planet's atmospheric

composition. Strong Rayleigh scattering in the optical wavelength is powerful evidence for a hydrogen-dominated atmosphere.

Rayleigh scattering occurs when light particles scatter in a medium without a change in wavelength.

Such scattering strongly depends on wavelength and enhances short wavelengths; it causes greater transit depth in the blue rather than in the red wavelength.

The team's observations showed that GJ 1214 b's atmosphere does not display strong Rayleigh scattering. This finding implies that the planet has a water-rich or a hydrogen-dominated atmosphere with extensive clouds.

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