Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A safety net for fast migrators: Interactions between gap-opening and
  sub-gap-opening bodies in a protoplanetary disk   Young planets interact with their parent gas disks through tidal torques. An
imbalance between inner and outer torques causes bodies of mass $\ga 0.1$ Earth
masses to lose angular momentum and migrate inward rapidly relative to the
disk; this is known as ``Type I'' migration. However, protoplanets that grow to
gas giant mass, O($10^2) M_\oplus$, open a gap in the disk and are subsequently
constrained to migrate more slowly, locked into the disk's viscous evolution in
what is called "Type II" migration. In a young planetary system, both Type I
and Type II bodies likely coexist; if so, differential migration ought to
result in close encounters when the former originate on orbits exterior to the
latter. We investigate the resulting dynamics, using two different numerical
approaches: an N-body code with dissipative forces added to simulate the effect
of the gas disk, and a hybrid code which combines an N-body component with a
1-dimensional viscous disk model, treating planet-disk interactions in a more
self-consistent manner. In both cases, we find that sub-gap-opening bodies have
a high likelihood of being resonantly captured when they encounter a
gap-opening body. A giant planet thus tends to act as a barrier in a
protoplanetary disk, collecting smaller protoplanets outside of its orbit. Such
behavior has two important implications for giant planet formation: First, for
captured protoplanets it mitigates the problem of the migration timescale
becoming shorter than the growth timescale. Secondly, it suggests one path to
forming systems with multiple giant planets: Once the first has formed, it
traps/accretes the future solid core of the second in an exterior mean-motion
resonance, and so on. The most critical step in giant planet formation may thus
be the formation of the very first one.

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The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con
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The categories of this paper are: q-fin