TRAPPIST-1

Forming The Trappist-1 System In Two Steps During The Recession Of The Disc Inner Edge

By Keith Cowing

Status Report

astro-ph.EP

August 27, 2024

Filed under exoplanet, Laplace angles, Protoplanetary Disk, TRAPPIST-1, TRAPPIST-1 b, TRAPPIST-1 c, TRAPPIST-1 e, TRAPPIST-1d, TRAPPIST-1f, TRAPPIST-1g, TRAPPIST-1h

Forming The Trappist-1 System In Two Steps During The Recession Of The Disc Inner Edge — Joining of the inner and outer subsystems. The evolution of the semi-major axes is shown with continuous coloured lines for all planets, which are also labelled by circles whose size reflect the observed size of the planets. In our favoured scenario, planet e followed the inner edge while planets b, c and d were in the inner cavity. Planets f, g and h join the system later, undergoing inward disc-driven migration (the disc is depicted by the top shaded area, with the lighter shading on the right indicating that the disc will eventually disperse). Since planet g is more massive than f and h, it is likely to capture f in resonance (the 4:3 being the favoured commensurability [5]) and the two planets migrate in together. When f reaches the 3:2 resonance with e, the combined push from g-f is sufficient to dislodge planet e from the inner edge (shown as a blue line enclosing the top shaded area). Driven by a full OLT, the orbit of planet e decays faster than f and g, approaching the 3:2 resonance with d. Planet h is the last one to migrate in and capture g in the 3:2 resonance to complete the chain. — astro-ph.EP

Trappist-1 hosts 7 planets where period ratios of neighbouring pairs are close to the 8:5, 5:3, 3:2, 3:2, 4:3, and 3:2 ratios in increasing distance from the star. The Laplace angles associated with neighbouring triplets are observed to be librating, proving the resonant nature of the system.

This compact, resonant configuration is a manifest sign of disc-driven migration; however, the preferred outcome of such evolution is the establishment of first-order resonances, not the high-order resonances observed in the inner system. Here, we explain the observed orbital configuration in a model that is largely independent on the specific disc migration and orbital circularisation efficiencies.

Together with migration, the two key elements of our model are: i) the inner border of the protoplanetary disc receded with time; and ii) the system was initially separated in two sub-systems. Specifically, the inner b, c d and e planets were initially placed in a 3:2 resonance chain and then evolved to the 8:5 — 5:3 commensurability between planets b, c and d under the effect of the recession of the inner edge of the disc, whereas the outer planets migrated to the inner edge at a later time, establishing the remaining resonances.

Our results pivot on the dynamical role of the presently unobservable recession of the inner edge of protoplanetary discs. They also reveal the role of recurring phases of convergent migration followed by resonant repulsion with associated orbital circularisation when resonant chains interact with migration barriers.

Gabriele Pichierri, Alessandro Morbidelli, Konstantin Batygin, Ramon Brasser

Comments: To appear in Nature Astronomy
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.08677 [astro-ph.EP] (or arXiv:2406.08677v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2406.08677
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Related DOI:
https://doi.org/10.1038/s41550-024-02342-4
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Submission history
From: Gabriele Pichierri
[v1] Wed, 12 Jun 2024 22:36:37 UTC (3,536 KB)
https://arxiv.org/abs/2406.08677

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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