Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Water Vapor and Clouds on the Habitable-Zone Sub-Neptune Exoplanet
  K2-18b   Results from the Kepler mission indicate that the occurrence rate of small
planets ($<3$ $R_\oplus$) in the habitable zone of nearby low-mass stars may be
as high as 80%. Despite this abundance, probing the conditions and atmospheric
properties on any habitable-zone planet is extremely difficult and has remained
elusive to date. Here, we report the detection of water vapor and the likely
presence of liquid and icy water clouds in the atmosphere of the $2.6$
$R_\oplus$ habitable-zone planet K2-18b. The simultaneous detection of water
vapor and clouds in the mid-atmosphere of K2-18b is particularly intriguing
because K2-18b receives virtually the same amount of total insolation from its
host star ($1368_{-107}^{+114}$ W m$^{-2}$) as the Earth receives from the Sun
(1361 W m$^{-2}$), resulting in the right conditions for water vapor to
condense and explain the detected clouds. In this study, we observed nine
transits of K2-18b using HST/WFC3 in order to achieve the necessary sensitivity
to detect the water vapor, and we supplement this data set with Spitzer and K2
observations to obtain a broader wavelength coverage. While the thick
hydrogen-dominated envelope we detect on K2-18b means that the planet is not a
true Earth analog, our observations demonstrate that low-mass habitable-zone
planets with the right conditions for liquid water are accessible with
state-of-the-art telescopes.

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The categories of this paper are: bayes-an
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg