Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Broadband Transmission Spectroscopy of the super-Earth GJ 1214b suggests
  a Low Mean Molecular Weight Atmosphere   We used WIRCam on CFHT to observe four transits of the super-Earth GJ 1214b
in the near-infrared. For each transit we observed in two bands
nearly-simultaneously by rapidly switching the WIRCam filter wheel back and
forth for the duration of the observations. By combining all our J-band (~1.25
microns) observations we find a transit depth in this band of 1.338\pm0.013% -
a value consistent with the optical transit depth reported by Charbonneau and
collaborators. However, our best-fit combined Ks-band (~2.15 microns) transit
depth is deeper: 1.438\pm0.019%. Formally our Ks-band transits are deeper than
the J-band transits observed simultaneously by a factor of 1.072\pm0.018 - a
4-sigma discrepancy. The most straightforward explanation for our deeper
Ks-band depth is a spectral absorption feature from the limb of the atmosphere
of the planet; for the spectral absorption feature to be this prominent the
atmosphere of GJ 1214b must have a large scale height and a low mean molecular
weight. That is, it would have to be hydrogen/helium dominated and this planet
would be better described as a mini-Neptune. However, recently published
observations from 0.78 - 1.0 microns, by Bean and collaborators, show a lack of
spectral features and transit depths consistent with those obtained by
Charbonneau and collaborators. The most likely atmospheric composition for GJ
1214b that arises from combining all these observations is less clear; if the
atmosphere of GJ 1214b is hydrogen/helium dominated then it must have either a
haze layer that is obscuring transit depth differences at shorter wavelengths,
or significantly different spectral features than current models predict. Our
observations disfavour a water-world composition, but such a composition will
remain a possibility until observations reconfirm our deeper Ks-band transit
depth or detect features at other wavelengths. [Abridged]

3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc