Outcomes of Grazing impacts between Sub-Neptunes in Kepler Multis

Project Author
Issue Date
Hwang, Jason A.
Chatterjee, Sourav
Lombardi, James C., Jr. (Jamie)
Steffen, Jason H.
Rasio, Frederic A.
Thumbnail Image
First Reader
Additional Readers
equation of state , hydrodynamics , methods: numerical , planets and satellites: dynamical evolution and stability , planets and satellites: gaseous planets , stars: individual (Kepler-36)
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/V-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.
This article has been accepted for publication in The Astrophysical Journal ©: 2018. Hwang, J., Chatterjee, S., Lombardi, J.C. Jr., Steffen, J.H., Rasio, F. Published by the American Astronomical Society. All rights reserved.
Hwang, J., Chatterjee, S., Lombardi, J.C. Jr., Steffen, J.H., and Rasio, F. (2018). Outcomes of Grazing Impacts between Sub-Neptunes in Kepler Multis. Astrophysical Journal 852(1): 1-24. Doi: 10.3847/1538-4357/aa9d42
Published article
Institute of Physics