Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How Deep Is the Ocean? Exploring the phase structure of water-rich
  sub-Neptunes   Understanding the internal structures of planets with a large H$_2$O
component is important for the characterisation of sub-Neptune planets. The
finding that the mini-Neptune K2-18b could host a liquid water ocean beneath a
mostly hydrogen envelope motivates a detailed examination of the phase
structures of water-rich planets. To this end, we present new internal
structure models for super-Earths and mini-Neptunes that enable detailed
characterisation of a planet's water component. We use our models to explore
the possible phase structures of water worlds and find that a diverse range of
interiors are possible, from oceans sandwiched between two layers of ice to
supercritical interiors beneath steam atmospheres. We determine how the bulk
properties and surface conditions of a water world affect its ocean depth,
finding that oceans can be up to hundreds of times deeper than on Earth. For
example, a planet with a 300 K surface can possess H$_2$O oceans with depths
from 30-500 km, depending on its mass and composition. We also constrain the
region of mass-radius space in which planets with H/He envelopes could host
liquid H$_2$O, noting that the liquid phase can persist at temperatures up to
647 K at high pressures of $218$-$7\times10^4$ bar. Such H/He envelopes could
contribute significantly to the planet radius while retaining liquid water at
the surface, depending on the planet mass and temperature profile. Our findings
highlight the exciting possibility that habitable conditions may be present on
planets much larger than Earth.

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The categories of this paper are: math
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The categories of this paper are: econ
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: patt-sol
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph