Context : GJ 1214 b is one of the few known transiting super-Earth-sized exoplanets with a measured mass and radius .
It orbits an M-dwarf , only 14.55 pc away , making it a favorable candidate for follow-up studies .
However , the composition of GJ 1214 b ’ s mysterious atmosphere has yet to be fully unveiled .

Aims : Our goal is to distinguish between the various proposed atmospheric models to explain the properties of GJ 1214 b : hydrogen-rich or hydrogen-He mix , or a heavy molecular weight atmosphere with reflecting high clouds , as latest studies have suggested .

Methods : Wavelength-dependent planetary radii measurements from the transit depths in the optical/NIR are the best tool to investigate the atmosphere of GJ 1214 b .
We present here ( i ) photometric transit observations with a narrow-band filter centered on 2.14 \mu m and a broad-band I -Bessel filter centered on 0.8665 \mu m , and ( ii ) transmission spectroscopy in the H and K atmospheric windows that cover three transits .
The obtained photometric and spectrophotometric time series were analyzed with MCMC simulations to measure the planetary radii as a function of wavelength .
We determined radii ratios of 0.1173 _ { -0.0024 } ^ { +0.0022 } for I -Bessel and 0.11735 _ { -0.00076 } ^ { +0.00072 } at 2.14 \mu m .

Results : Our measurements indicate a flat transmission spectrum , in agreement with last atmospheric models that favor featureless spectra with clouds and high molecular weight compositions .

Conclusions :