September 15, 2013

Gliese 1214b likely has a water-rich atmosphere.

Gliese 1214b is about 2.7 times Earth’s diameter and is almost 7 times as massive. It is located 42 light years away in the constellation Ophiuchus.

The Japanese researchers used the 8.2 meter Subaru telescope to make the find.

Super-earths are an emerging population of extrasolar planets whose masses and radii lie between those of the Earth and the Uranus/Neptune. The nature of super-Earths, such as internal structure and atmospheric compositions, remains almost unknown since there is no super-Earth in our Solar System. Transiting super-Earths are thus invaluable targets for observations to learn the nature of super-Earths in details.

GJ 1214b discovered by Charbonneau et al. (2009) is the first-ever transiting super-Earth around an M dwarf which enables us to study its atmosphere through so-called transmission spectroscopy, thanks to the small host star’s size (1/5th the radius of our sun).

Arxiv - Multi-Color Transit Photometry of GJ 1214b through BJHKs-Bands and a Long-Term Monitoring of the Stellar Variability of GJ 1214

The article is also in the Astrophysical journal

Future Observation suggestions

Although our results have suggested that GJ 1214b has a fairly flat transmission spectrum through BJHKs-bands, it is still difficult to determine one decisive atmosphere model. Experiences have shown that broadband sinwgle-color transit photometry is not efficient to constrain an atmosphere model in the presence of starspots and the stellar variability. More effective ways to characterize atmospheres of transiting planets would be

(1) simultaneous multi-band transit photometry using small-medium ground-based telescopes
(2) multi-object spectro-photometry using large groundbased telescopes
(3) spectro-photometry using space telescopes.

It would be important to observe the wavelength region where the difference of transit depths between the low-µ and the high-µ atmospheres is significant, especially the Rayleigh slope (optical) region and around K-band region. In addition, repeated transit observations are highly desirable to improve the significance and to check possible time variations. As the ongoing ground-based transit surveys (e.g., MEarth) and the future space-based survey like TESS (Ricker et al. 2010) will discover more transiting super-Earths around nearby cool host stars, the current experiences for GJ 1214b would become a good practice for the future.

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