Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Tidal evolution of exoplanetary systems hosting Potentially Habitable
  Exoplanets. The cases of LHS-1140 b-c and K2-18 b-c   We present a model to study secularly and tidally evolving three-body systems
composed by two low-mass planets orbiting a star, in the case where the bodies
rotation axes are always perpendicular to the orbital plane. The tidal theory
allows us to study the spin and orbit evolution of both stiff Earth-like
planets and predominantly gaseous Neptune-like planets. The model is applied to
study two recently-discovered exoplanetary systems containing potentially
habitable exoplanets (PHE): LHS-1140 b-c and K2-18 b-c. For the former system,
we show that both LHS-1140 b and c must be in nearly-circular orbits. For K2-18
b-c, the combined analysis of orbital evolution timescales with the current
eccentricity estimation of K2-18 b allows us to conclude that the inner planet
(K2-18 c) must be a Neptune-like gaseous body. Only this would allow for the
eccentricity of K2-18 b to be in the range of values estimated in recent works
($e=0.20 \pm 0.08$), provided that the uniform viscosity coefficient of K2-18 b
is greater than $2.4 \times 10^{19} \ \textrm{Pa s}$ (which is a value
characteristic of stiff bodies) and supposing that such system has an age of
some Gyr.

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The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
3
The categories of this paper are: physics
2
The categories of this paper are: math