2024/09/09 by Donald Liveoak, Sarah Millholland, Liveoak, Donald +1 · 1 citation
Earth and Planetary Sciences · Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #High-pressure geophysics and materials
paper · pdf · doi:10.48550/arxiv.2409.05748
openalex publication_date 2024/09/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Conventional planet formation theories predict a paucity of massive planets around small stars, especially very low-mass (0.1 - 0.3 M\odot) mid-to-late M dwarfs. Such tiny stars are expected to form planets of terrestrial sizes, but not much bigger. However, this expectation is challenged by the recent discovery of LHS 3154 b, a planet with period of 3.7 days and minimum mass of 13.2 M⊕ orbiting a 0.11 M\odot star. Here, we propose that close-in Neptune-mass planets like LHS 3154 b formed through an anomalous series of mergers from a primordial compact system of super-Earths. We perform simulations within the context of the "breaking the chains" scenario, in which super-Earths initially form in tightly-spaced chains of mean-motion resonances before experiencing dynamical instabilities and collisions. Planets as massive and close-in as LHS 3154 b (Mp ∼ 12 - 20 M⊕, P < 7 days) are produced in ∼1% of simulated systems, in broad agreement with their low observed occurrence. These results suggest that such planets do not require particularly unusual formation conditions but rather are an occasional byproduct of a process that is already theorized to explain compact multi-planet systems. Interestingly, our simulated systems with LHS 3154 b-like planets also contain smaller planets at around ∼ 30 days, offering a possible test of this hypothesis.