Planet Formation by Gas-Assisted Accretion of Small Solids
The Astrophysical Journal(2024)
摘要
We compute the accretion efficiency of small solids, with radii 1 cm ≤ Rs
≤ 10 m, on planets embedded in gaseous disks. Planets have masses 3 ≤
Mp ≤ 20 Earth masses (Me) and orbit within 10 AU of a solar-mass star. Disk
thermodynamics is modeled via three-dimensional radiation-hydrodynamic
calculations that typically resolve the planetary envelopes. Both icy and rocky
solids are considered, explicitly modeling their thermodynamic evolution.
Maximum efficiencies of 1 ≤ Rs ≤ 100 cm particles are generally
≲ 10
segregated beyond the planet's orbit. A simplified approach is applied to
compute the accretion efficiency of small cores, with masses Mp ≤ 1 Me and
without envelopes, for which efficiencies are approximately proportional to
Mp^(2/3). The mass flux of solids, estimated from unperturbed drag-induced
drift velocities, provides typical accretion rates dMp/dt ≲ 1e-5
Mearth/yr. In representative disk models with an initial gas-to-dust mass ratio
of 70-100 and total mass of 0.05-0.06 Msun, solids' accretion falls below 1e-6
Mearth/yr after 1-1.5 million years (Myr). The derived accretion rates, as
functions of time and planet mass, are applied to formation calculations that
compute dust opacity self-consistently with the delivery of solids to the
envelope. Assuming dust-to-solid coagulation times of approximately 0.3 Myr and
disk lifetimes of approximately 3.5 Myr, heavy-element inventories in the range
3-7 Me require that approximately 90-150 Me of solids cross the planet's orbit.
The formation calculations encompass a variety of outcomes, from planets a few
times the Earth mass, predominantly composed of heavy elements, to giant
planets. Peak luminosities during the epoch of solids' accretion range from
≈ 1e-7 to ≈ 1e-6 times the solar luminosity.
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关键词
Stellar accretion disks,Radiative magnetohydrodynamics,Astrophysical fluid dynamics,Computational methods,Planet formation,Planetary-disk interactions
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