Outcomes of Sub-Neptune Collisions

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Issue Date
2024-12-01
Authors
Ghosh, Tuhin
Chatterjee, Sourav
Lombardi, James C., Jr. (Jamie)
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Exoplanets , Hydrodynamical simulations , Exoplanet structure , Extrasolar gaseous planets , Exoplanet dynamics , N-body simulations
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Abstract
Observed high multiplicity planetary systems are often tightly packed. Numerical studies indicate that such systems are susceptible to dynamical instabilities. Dynamical instabilities in close-in tightly packed systems, similar to those found in abundance by Kepler, often lead to planet-planet collisions. For sub-Neptunes, the dominant type of observed exoplanets, the planetary mass is concentrated in a rocky core, but the volume is dominated by a low-density gaseous envelope. For these, using the traditional perfect merger assumption (also known as the 'sticky-sphere' approximation) to resolve collisions is questionable. Using both N-body integration and smoothed-particle hydrodynamics, we have simulated sub-Neptune collisions for a wide range in realistic kinematic properties such as impact parameters (๐‘) and impact velocities (๐‘ฃ) to study the possible outcomes in detail. We find that the majority of the collisions with kinematic properties similar to what is expected from dynamical instabilities in multiplanet systems may not lead to mergers of sub-Neptunes. Instead, both sub-Neptunes survive the encounter, often with significant atmosphere loss. When mergers do occur, they can involve significant mass loss and can sometimes lead to complete disruption of one or both planets. Sub-Neptunes merge or disrupt if ๐‘ < ๐‘๐‘สณโฑแต—, a critical value dependent on ๐‘ฃ/๐‘ฃโ‚‘โ‚›๐šŒ, where ๐‘ฃโ‚‘โ‚›๐šŒ is the escape velocity from the surface of the hypothetical merged planet assuming perfect merger. For ๐‘ฃ/๐‘ฃโ‚‘โ‚›๐šŒ โ‰ฒ 2.5, ๐‘๐‘สณโฑแต— โˆ (๐‘ฃ/๐‘ฃโ‚‘โ‚›๐šŒ)โปยฒ, and collisions with ๐‘ < ๐‘๐‘สณโฑแต— typically lead to mergers. On the other hand, for ๐‘ฃ/๐‘ฃโ‚‘โ‚›๐šŒ โ‰ณ 2.5, ๐‘๐‘สณโฑแต— โˆ ๐‘ฃ/๐‘ฃโ‚‘โ‚›๐šŒ, and the collisions with ๐‘ < ๐‘๐‘สณโฑแต— can result in complete destruction of one or both sub-Neptunes.
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Physics
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ยฉ 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Citation
Tuhin Ghosh et al 2024 AJ 168 238
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Published version
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IOP Publishing Ltd
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