GJ 1214 is a nearby M dwarf star that hosts a transiting super-Earth-size planet , making this system an excellent target for atmospheric studies .
Most studies find that the transmission spectrum of GJ 1214b is flat , which favors either a high mean molecular weight or cloudy/hazy hydrogen ( H ) rich atmosphere model .
Photometry at short wavelengths ( < 0.7 \mu m ) and in the K -band can discriminate the most between these different atmosphere models for GJ 1214b , but current observations do not have sufficiently high precision .
We present photometry of seven transits of GJ 1214b through a narrow K -band ( 2.141 \mu m ) filter with the Wide Field Camera on the 3.8 m United Kingdom Infrared Telescope .
Our photometric precision is typically 1.7 \times 10 ^ { -3 } ( for a single transit ) , comparable with other ground-based observations of GJ 1214b .
We measure a planet-star radius ratio of 0.1158 \pm 0.0013 , which , along with other studies , also supports a flat transmission spectrum for GJ 1214b .
Since this does not exclude a scenario where GJ 1214b has a H-rich envelope with heavy elements that are sequestered below a cloud/haze layer , we compare K -band observations with models of H _ { 2 } collision-induced absorption in an atmosphere for a range of temperatures .
While we find no evidence for deviation from a flat spectrum ( slope s = 0.0016 \pm 0.0038 ) , an H _ { 2 } dominated upper atmosphere ( < 60 mbar ) can not be excluded .
More precise observations at < 0.7 \mu m and in the K -band as well as a uniform analysis of all published data would be useful for establishing more robust limits on atmosphere models for GJ 1214b .