Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Formation of Uranus and Neptune: Fine Tuning in Core Accretion   Uranus and Neptune are ice giants with $\sim$ 15% atmospheres by mass,
placing them in an intermediate category between rocky planets and gas giants.
These atmospheres are too massive to have been primarily outgassed, yet they
never underwent runaway gas accretion. The ice giants never reached critical
core mass ($M_\text{crit}$) in a full gas disk, yet their cores are $\gtrsim
M_\text{crit}$, suggesting that their envelopes were mainly accreted at the end
of the disk lifetime. Pebble accretion calls into question traditional slow
atmospheric growth during this phase. We show that the full-sized ice giants
predominantly accreted gas from a disk depleted by at least a factor of $\sim
100$. Such a disk dissipates in $ \lesssim 10^5$ years. Why would both cores
stay sub-critical for the entire $\sim$ Myr disk lifetime, only to reach
$M_\text{crit}$ in the final $10^5$ years? This is fine tuned. Ice giants in
the outer disk have atmospheric mass fractions comparable to the disk
gas-to-solid ratio during the bulk of their gas accretion. This point in disk
evolution coincides with a dynamical upheaval: the gas loses its ability to
efficiently damp the cores' random velocities, allowing them to be
gravitationally excited by Jupiter and Saturn. We suggest that the ice giants'
cores began growing on closer-in orbits (staying sub-critical), and migrated
out during this dynamical instability. There, their orbits circularized after
accreting much of their mass in solids. Finally, they accreted their envelopes
from a depleted nebula, where the sparseness of feeding zone gas prevented
runaway.

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The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: math
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess