  The newly discovered planet GJ 1214b is the first known transiting
super-Earth requiring a significant atmosphere to explain its observed mass and
radius. Models for the structure of this planet predict that it likely
possesses a H-He envelope of at least 0.05% of the total mass of the planet.
However, models without a significant H-He atmosphere are not entirely ruled
out by the available data. Here we explore a range of possible atmospheres for
the planet, ranging from solar composition gas, to pure CO_2 or water (steam).
We present transmission and emission spectra for each of these cases. We find
that, if GJ 1214b possesses a hydrogen-rich atmosphere as expected, then the
primary transit depth for such an atmosphere would vary at a level of up to
0.3% as a function of wavelength, relative to the background light of its
M-dwarf host star. Observations at this level of precision are potentially
obtainable with current space-based instrumentation. Successful detection of
the transmission signature of this planet at the ~0.1% level would therefore
provide confirmation of the hydrogen-rich nature of the planetary atmosphere.
It follows that transmission spectroscopy at this level of precision could
provide a first glimpse into answering the question of whether planets in the
super-Earth mass regime (1 - 10 M_Earth) more closely resemble large
terrestrial planets or small gas giant planets.
