Binary planet formation by gas-assisted encounters of planetary embryos

Abstract

We present radiation hydrodynamic simulations in which binary planets form by close encounters in a system of several super-Earth embryos. The embryos are embedded in a protoplanetary disk consisting of gas and pebbles and evolve in a region where the disk structure supports convergent migration due to Type I torques. As the embryos accrete pebbles, they become heated and thus affected by the thermal torque (Benítez-Llambay et al. 2015) and the hot-trail effect (Chrenko et al. 2017) which excites orbital eccentricities. Motivated by findings of Eklund & Masset (2017), we assume the hot-trail effect operates also vertically and reduces the efficiency of inclination damping. Non-zero inclinations allow the embryos to become closely packed and also vertically stirred within the convergence zone. Subsequently, close encounters of two embryos assisted by the disk gravity can form transient binary planets which quickly dissolve. Binary planets with a longer lifetime $\sim$$10^4$ yr form in 3-body interactions of a transient pair with one of the remaining embryos. The separation of binary components generally decreases in subsequent encounters and due to pebble accretion until the binary merges, forming a giant planet core. We provide an order-of-magnitude estimate of the expected occurrence rate of binary planets, yielding one binary planet per $\simeq$$2$--$5\times 10^4$ planetary systems. Therefore, although rare, the binary planets may exist in exoplanetary systems and they should be systematically searched for.

arXiv commentAccepted for publication in ApJ, 18 pages, 10 figures

References in corpus (75)

• Spectral Energy Distributions of T Tauri Stars With Passive Circumstellar Disks
• REBOUND: An open-source multi-purpose N-body code for collisional dynamics
• Using FU Orionis Outbursts to Constrain Self-Regulated Protostellar Disk Models
• Rapid growth of gas-giant cores by pebble accretion
• A simple model for the evolution of the dust population in protoplanetary disks
• IAS15: A fast, adaptive, high-order integrator for gravitational dynamics, accurate to machine precision over a billion orbits
• Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
• The effect of gas drag on the growth of protoplanets -- Analytical expressions for the accretion of small bodies in laminar disks
• FARGO: a fast eulerian transport algorithm for differentially rotating disks
• A torque formula for non-isothermal Type I planetary migration - II. Effects of diffusion
• Forming the cores of giant planets from the radial pebble flux in protoplanetary discs
• Separating gas-giant and ice-giant planets by halting pebble accretion
• A torque formula for non-isothermal Type I planetary migration - I. Unsaturated horseshoe drag
• A comparative study of disc-planet interaction
• Timescale of Mass Accretion in Pre-Main-Sequence Stars
• Breaking the Chains: Hot Super-Earth systems from migration and disruption of compact resonant chains
• On the orbital evolution and growth of protoplanets embedded in a gaseous disc
• Pebble isolation mass --- scaling law and implications for the formation of super-Earths and gas giants
• Transit timing effects due to an exomoon
• Three-dimensional simulations of multiple protoplanets embedded in a protostellar disc
• On the corotation torque in a radiatively inefficient disk
• Formation of Kuiper Belt Binaries
• Formation of Kuiper Belt Binaries by Gravitational Collapse
• Dynamics of pebbles in the vicinity of a growing planetary embryo: hydro-dynamical simulations
• Planet migration in three-dimensional radiative discs
• The Hunt for Exomoons with Kepler (HEK): I. Description of a New Observational Project
• Migration of Protoplanets in Radiative Disks
• Planet heating prevents inward migration of planetary cores
• A Sub-Earth-Mass Moon Orbiting a Gas Giant Primary or a High Velocity Planetary System in the Galactic Bulge
• Stellar irradiated discs and implications on migration of embedded planets I: equilibrium discs
• The co-orbital corotation torque in a viscous disk: numerical simulations
• Low-Mass Proto-Planet Migration in T-Tauri Alpha-Disks
• Evidence for Two Populations of Classical Transneptunian Objects: The Strong Inclination Dependence of Classical Binaries
• Reduced gas accretion on super-Earths and ice giants
• On the evolution of eccentric and inclined protoplanets embedded in protoplanetary disks
• Hot super-Earths and giant planet cores from different migration histories
• 3D-radiation hydro simulations of disk-planet interactions: I. Numerical algorithm and test cases
• Treating gravity in thin disk simulations
• Extrasolar Trojans: The Viability and Detectability of Planets in the 1:1 Resonance
• Migration of Earth-size planets in 3D radiative discs
• Thermo-Hydrodynamics of Circumstellar Disks with High-mass Planets
• A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus
• SPH calculations of asteroid disruptions: The role of pressure dependent failure models
• HEK VI: On the Dearth of Galilean Analogs in Kepler and the Exomoon Candidate Kepler-1625b I
• Satellites of the largest Kuiper belt objects
• Determination of the size, mass, and density of "exomoons" from photometric transit timing variations
• Coorbital thermal torques on low-mass protoplanets
• On the corotation torque for low-mass eccentric planets
• Influence of an inner disc on the orbital evolution of massive planets migrating in resonance
• Growing and moving low-mass planets in non-isothermal disks
• The Hunt for Exomoons with Kepler (HEK): V. A Survey of 41 Planetary Candidates for Exomoons
• Formation of Kuiper-belt binaries through multiple chaotic scattering encounters with low-mass intruders
• All planetesimals born near the Kuiper Belt formed as binaries
• Main Belt Binary Asteroidal Systems With Circular Mutual Orbits
• On the detection of Exomoons: A search in Kepler data for the orbital sampling effect and the scatter peak
• Detecting extrasolar moons akin to solar system satellites with an orbital sampling effect
• Signals of exomoons in averaged light curves of exoplanets
• Torques Induced by Scattered Pebble-flow in Protoplanetary Disks
• Early Dynamical Instabilities in the Giant Planet Systems
• Microlensing Detections of Moons of Exoplanets
• Extrasolar Binary Planets I: Formation by tidal capture during planet-planet scattering
• Detectability of extrasolar moons as gravitational microlenses
• Origin and Detectability of coorbital planets from radial velocity data
• Transit of Exomoon Plasma Tori: New Diagnosis
• Evolution of eccentricity and inclination of hot protoplanets embedded in radiative discs
• Complete spin and orbital evolution of close-in bodies using a Maxwell viscoelastic rheology
• Convergence zones for Type I migration: an inward shift for multiple planet systems
• Fast migration of low-mass planets in radiative discs
• Eccentricity excitation and merging of planetary embryos heated by pebble accretion
• Dynamical friction on hot bodies in opaque, gaseous media
• The nature of the giant exomoon candidate Kepler-1625 b-i
• Making giant planet cores: convergent migration and growth of planetary embryos in non-isothermal discs
• Extrasolar Binary Planets II: Detectability by Transit Observations
• Time evolution of a viscous protoplanetary disk with a free geometry: toward a more self-consistent picture
• Binary Candidates in the Jovian Trojan and Hilda Populations from NEOWISE Lightcurves

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