Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Enceladus's measured physical libration requires a global subsurface
  ocean   Several planetary satellites apparently have subsurface seas that are of
great interest for, among other reasons, their possible habitability. The
geologically diverse Saturnian satellite Enceladus vigorously vents liquid
water and vapor from fractures within a south polar depression and thus must
have a liquid reservoir or active melting. However, the extent and location of
any subsurface liquid region is not directly observable. We use measurements of
control points across the surface of Enceladus accumulated over seven years of
spacecraft observations to determine the satellite's precise rotation state,
finding a forced physical libration of 0.120 $\pm$ 0.014{\deg} (2{\sigma}).
This value is too large to be consistent with Enceladus's core being rigidly
connected to its surface, and thus implies the presence of a global ocean
rather than a localized polar sea. The maintenance of a global ocean within
Enceladus is problematic according to many thermal models and so may constrain
satellite properties or require a surprisingly dissipative Saturn.

35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs