Exoplanets & Exomoons

Early Stages Of Gap Opening By Planets In Protoplanetary Discs

By Keith Cowing
Status Report
July 9, 2024
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Early Stages Of Gap Opening By Planets In Protoplanetary Discs
ALMA image of the protoplanetary disk surrounding the young star HD 163296 as seen in dust. IMAGE CREDIT: ALMA: ESO/NAOJ/NRAO; A. ISELLA; B. SAXTON NRAO/AUI/NSF.

Annular substructures in protoplanetary discs, ubiquitous in sub-mm observations, can be caused by gravitational coupling between a disc and its embedded planets.

Planetary density waves inject angular momentum into the disc leading to gap opening only after travelling some distance and steepening into shocks (in the absence of linear damping); no angular momentum is deposited in the planetary coorbital region, where the wave has not shocked yet. Despite that, simulations show mass evacuation from the coorbital region even in inviscid discs, leading to smooth, double-trough gap profiles.

Here we consider the early, time-dependent stages of planetary gap opening in inviscid discs. We find that an often-overlooked contribution to the angular momentum balance caused by the time-variability of the specific angular momentum of the disc fluid (caused, in turn, by the time-variability of the radial pressure support) plays a key role in gap opening.

Focusing on the regime of shallow gaps with depths of ≲20%, we demonstrate analytically that early gap opening is a self-similar process, with the amplitude of the planet-driven perturbation growing linearly in time and the radial gap profile that can be computed semi-analytically.

We show that mass indeed gets evacuated from the coorbital region even in inviscid discs. This evolution pattern holds even in viscous discs over a limited period of time. These results are found to be in excellent agreement with 2D numerical simulations. Our simple gap evolution solutions can be used in studies of dust dynamics near planets and for interpreting protoplanetary disc observations.

Amelia J. Cordwell, Roman R. Rafikov

Comments: 20 pages, 16 figures, submitted to MNRAS, comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2407.01728 [astro-ph.EP] (or arXiv:2407.01728v1 [astro-ph.EP] for this version)
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Submission history
From: Amelia J. Cordwell
[v1] Mon, 1 Jul 2024 19:01:20 UTC (2,548 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻