Exoplanetology: Exoplanets & Exomoons

Origin Of Compact Exoplanetary Systems During Disk Infall

By Keith Cowing
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astro-ph.EP
June 4, 2025
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Origin Of Compact Exoplanetary Systems During Disk Infall
Estimated total mass of transiting compact systems, Mtot, scaled to the stellar mass, M∗. a, (Mtot/M∗) for compact systems having ≥ 3 known planets that orbit a single star within a < 0.5 au (circle markers, blue box). Points are ordered left-to-right by ascending stellar mass. Data are from www.exoplanetarchive.ipac.caltech.edu. For cases without mass estimates, we use the observed planet radius, increase the estimated radius uncertainty by a factor of 2, and then apply a radius vs. mass relation [46]. Light [medium] blue circles are systems with all [some] planetary masses estimated from this relation, while dark blue circles are systems with measured planetary masses. We include only systems with resulting errors ∆Mtot/Mtot < 1. b, Distribution of compact system mass ratios. Over a wide range of stellar masses (M∗ ∼ 0.1 to 1.3 stellar mass), compact multi-planet systems display a common mass ratio, with 90% of systems having 3×10−5 < (Mtot/M∗) < 3×10−4 (gray shaded region). This mass ratio is more similar to that of the gas giant satellite systems (square markers, yellow box) than to the inner or outer planets in our Solar System (triangle markers, red box). -- astro-ph.EP

Exoplanetary systems that contain multiple planets on short-period orbits appear to be prevalent in the current observed exoplanetary population, yet the processes that give rise to such configurations remain poorly understood.

A common prior assumption is that planetary accretion commences after the infall of gas and solids to the circumstellar disk ended. However, observational evidence indicates that accretion may begin earlier.

We propose that compact systems are surviving remnants of planet accretion that occurred during the final phases of infall. In regions of the disk experiencing ongoing infall, the planetary mass is set by the balance between accretion of infalling solids and the increasingly rapid inward migration driven by the surrounding gas as the planet grows.

This balance selects for similarly-sized planets whose mass is a function of infall and disk conditions. We show that infall-produced planets can survive until the gas disk disperses and migration ends, and that across a broad range of conditions, the mass of surviving systems is regulated to a few 10-5 to 10-4 times the host star’s mass. This provides an explanation for the similar mass ratios of known compact systems.

Raluca Rufu, Robin M. Canup

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Space Physics (physics.space-ph)
Cite as: arXiv:2505.22806 [astro-ph.EP](or arXiv:2505.22806v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2505.22806
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Journal reference: Nat Commun 16, 4853 (2025)
Related DOI:
https://doi.org/10.1038/s41467-025-60017-8
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Submission history
From: Raluca Rufu
[v1] Wed, 28 May 2025 19:27:30 UTC (6,720 KB)
https://arxiv.org/abs/2505.22806
Astrobiology,

Keith Cowing

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) 🖖🏻

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