Free-Floating Planets, Survivor Planets, Captured Planets and Binary Planets from Stellar Flybys

Abstract

In star clusters, close stellar encounters can strongly impact the architecture of a planetary system or even destroy it. We present a systematic study on the effects of stellar flybys on two-planet systems. When such a system experiences flybys, one or both planets can be ejected, forming free-floating planets (FFPs), captured planets (CPs) around the flyby star, and free-floating binary planets (BPs); the remaining single-surviving-planets (SSPs) can have their orbital radii and eccentricities greatly changed. Through numerical experiments, we calculate the formation fractions (or branching ratios) of FFPs, SSPs, CPs and BPs as a function of the pericenter distance of the flyby, and use them to derive analytical expressions for the formation rates of FFPs, SSPs, CPs and BPs in general cluster environments. We find that the production rates of FFPs and SSPs are similar (for initial planet semi-major axis ratio $a_1/a_2=0.6-0.8$), while the rate for CPs is a few times smaller. The formation fraction of BPs depends strongly on $a_1/a_2$ and on the planet masses. For Jupiter-mass planets, the formation fraction of BPs is always less than $1\%$ (for $a_1/a_2=0.8$) and typically much smaller ($\lesssim 0.2\%$ for $a_1/a_2\lesssim 0.7$). The fraction remains less than $1\%$ when considering $4M_{\mathrm{J}}$ planets. Overall, when averaging over all flybys, the production rate of BPs is less than $0.1\%$ of that for FFPs. We also derive the velocity distribution of FFPs produced by stellar flybys, and the orbital parameter distributions of SSPs, CPs and BPs. These results can be used in future studies of exotic planets (including FFPs) and planetary systems.

21 pages, 13+9 figures, accepted to ApJ

References in corpus (27)

• The NumPy array: a structure for efficient numerical computation
• REBOUND: An open-source multi-purpose N-body code for collisional dynamics
• Dynamical Outcomes of Planet-Planet Scattering
• IAS15: A fast, adaptive, high-order integrator for gravitational dynamics, accurate to machine precision over a billion orbits
• Analytical theory for the initial mass function: CO clumps and prestellar cores
• Dynamical Origin of Extrasolar Planet Eccentricity Distribution
• The effects of fly-bys on planetary systems
• Post-Oligarchic Evolution of Protoplanetary Embryos and the Stability of Planetary Systems
• The minimum mass for star formation, and the origin of binary brown dwarfs
• The Kinematics of the Scorpius-Centaurus OB Association from Gaia DR1
• New isolated planetary mass objects and the stellar and substellar mass function of the sigma Orionis cluster
• Scattering outcomes of close-in planets: constraints on planet migration
• The effects of dynamical interactions on planets in young substructured star clusters
• A rich population of free-floating planets in the Upper Scorpius young stellar association
• Stability of Multiplanetary Systems in Star Clusters
• Substellar Objects in Nearby Young Clusters (SONYC) VI: The planetary-mass domain of NGC1333
• Survivability of planetary systems in young and dense star clusters
• A terrestrial-mass rogue planet candidate detected in the shortest-timescale microlensing event
• Hill stability in the AMD framework
• In-Situ Scattering of Warm Jupiters and Implications for Dynamical Histories
• Spectroscopic Confirmation of the Least Massive Known Brown Dwarf in Chamaeleon
• KMT-2017-BLG-2820 and the Nature of the Free-Floating Planet Population
• Giant Planet Scatterings and Collisions: Hydrodynamics, Merger-Ejection Branching Ratio, and Properties of the Remnants
• On the Correlation between Hot Jupiters and Stellar Clustering: High-eccentricity Migration Induced by Stellar Flybys
• Fly-by encounters between two planetary systems II: Exploring the interactions of diverse planetary system architectures
• Infrared Spectroscopy of free-floating planet candidates in Upper Scorpius and Ophiuchus
• The Impact of Stellar Clustering on the Observed Multiplicity of Super-Earth systems: Outside-in Cascade of Orbital Misalignments Initiated by Stellar Flybys

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• Dynamical Instability of Multi-planet Systems and Free-floating Planets
• Why Wide Jupiter-Mass Binary-Objects Cannot Form
• Disk fraction among free-floating planetary-mass objects in Upper Scorpius