Outcomes of Sub-Neptune Collisions
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Author(s)
Ghosh, Tuhin
Chatterjee, Sourav
Lombardi, James C., Jr. (Jamie)
Date Issued
December 1, 2024
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 (𝑏) and impact velocities (𝑣) 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 𝑏 < 𝑏𝑐ʳⁱᵗ, a critical value dependent on 𝑣/𝑣ₑₛ𝚌, where 𝑣ₑₛ𝚌 is the escape velocity from the surface of the hypothetical merged planet assuming perfect merger. For 𝑣/𝑣ₑₛ𝚌 ≲ 2.5, 𝑏𝑐ʳⁱᵗ ∝ (𝑣/𝑣ₑₛ𝚌)⁻², and collisions with 𝑏 < 𝑏𝑐ʳⁱᵗ typically lead to mergers. On the other hand, for 𝑣/𝑣ₑₛ𝚌 ≳ 2.5, 𝑏𝑐ʳⁱᵗ ∝ 𝑣/𝑣ₑₛ𝚌, and the collisions with 𝑏 < 𝑏𝑐ʳⁱᵗ can result in complete destruction of one or both sub-Neptunes.
Journal
Astronomical Journal
Department
Physics
Citation
Tuhin Ghosh et al 2024 AJ 168 238
Publisher
IOP Publishing Ltd
Version of Article
Published version
DOI
10.3847/1538-3881/ad7d8a
ISSN
0004-6256
1538-3881
Rights
© 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.
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