TY - JOUR

T1 - Outcomes of Grazing Impacts between Sub-Neptunes in Kepler Multis

AU - Hwang, Jason

AU - Chatterjee, Sourav

AU - Lombardi, James

AU - Steffen, Jason H.

AU - Rasio, Frederic

N1 - Funding Information:
This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. F.A.R. and J.A.H. were supported by NASA Grant NNX12AI86G. J.A.H. was also supported by an NSF GK-12 Fellowship funded through NSF Award DGE-0948017 to Northwestern University. J.C.L. was supported by NSF grant number AST-1313091.
Funding Information:
This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. F.A.R. and J.A.H. were supported by NASA Grant NNX12AI86G. J.A.H. was also supported by an NSF GK-12 Fellowship funded through NSF Award DGE-0948017 to Northwestern University. J.C.L. was supported by NSF grant number AST-1313091. J.H.S. was supported by NASA grants NNX16AK08G and NNX16AK32G. We thank Joshua Fixelle for useful discussions while developing the equations of state used in the SPH calculations and Francesca Valsecchi for help with using MESA to generate sub-Neptune envelopes. We thank the anonymous referee for providing very thorough and helpful feedback leading to major improvements in this manuscript. This work used the SPLASH visualization software (Price 2007).

PY - 2018/1/1

Y1 - 2018/1/1

N2 - Studies of high-multiplicity, tightly packed planetary systems suggest that dynamical instabilities are common and affect both the orbits and planet structures, where the compact orbits and typically low densities make physical collisions likely outcomes. Since the structure of many of these planets is such that the mass is dominated by a rocky core, but the volume is dominated by a tenuous gas envelope, the sticky-sphere approximation, used in dynamical integrators, may be a poor model for these collisions. We perform five sets of collision calculations, including detailed hydrodynamics, sampling mass ratios, and core mass fractions typical in Kepler Multis. In our primary set of calculations, we use Kepler-36 as a nominal remnant system, as the two planets have a small dynamical separation and an extreme density ratio. We use an N-body code, Mercury 6.2, to integrate initially unstable systems and study the resultant collisions in detail. We use these collisions, focusing on grazing collisions, in combination with realistic planet models created using gas profiles from Modules for Experiments in Stellar Astrophysics and core profiles using equations of state from Seager et al. to perform hydrodynamic calculations, finding scatterings, mergers, and even a potential planet-planet binary. We dynamically integrate the remnant systems, examine the stability, and estimate the final densities, finding that the remnant densities are sensitive to the core masses, and collisions result in generally more stable systems. We provide prescriptions for predicting the outcomes and modeling the changes in mass and orbits following collisions for general use in dynamical integrators.

AB - Studies of high-multiplicity, tightly packed planetary systems suggest that dynamical instabilities are common and affect both the orbits and planet structures, where the compact orbits and typically low densities make physical collisions likely outcomes. Since the structure of many of these planets is such that the mass is dominated by a rocky core, but the volume is dominated by a tenuous gas envelope, the sticky-sphere approximation, used in dynamical integrators, may be a poor model for these collisions. We perform five sets of collision calculations, including detailed hydrodynamics, sampling mass ratios, and core mass fractions typical in Kepler Multis. In our primary set of calculations, we use Kepler-36 as a nominal remnant system, as the two planets have a small dynamical separation and an extreme density ratio. We use an N-body code, Mercury 6.2, to integrate initially unstable systems and study the resultant collisions in detail. We use these collisions, focusing on grazing collisions, in combination with realistic planet models created using gas profiles from Modules for Experiments in Stellar Astrophysics and core profiles using equations of state from Seager et al. to perform hydrodynamic calculations, finding scatterings, mergers, and even a potential planet-planet binary. We dynamically integrate the remnant systems, examine the stability, and estimate the final densities, finding that the remnant densities are sensitive to the core masses, and collisions result in generally more stable systems. We provide prescriptions for predicting the outcomes and modeling the changes in mass and orbits following collisions for general use in dynamical integrators.

KW - equation of state

KW - hydrodynamics

KW - methods: numerical

KW - planets and satellites: dynamical evolution and stability

KW - planets and satellites: gaseous planets

KW - stars: individual (Kepler-36)

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U2 - 10.3847/1538-4357/aa9d42

DO - 10.3847/1538-4357/aa9d42

M3 - Article

AN - SCOPUS:85040334224

VL - 852

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 41

ER -