2021/07/07 by Juliette Becker, Juliette C. Becker, Konstantin Batygin +2 · 1 citation
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Gas giant #Giant planet #Planet #Planetary migration #Planetary system #RADIUS #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/ac111e
accepted to ApJ; 13 pages, 6 figures
arxiv created 2021/07/07 · openalex created_date 2021/07/19 · openalex publication_date 2021/09/28 · arxiv updated 2021/10/04 · openalex updated_date 2026/08/05
Abstract Ultra-short-period (USP) planets reside inside the expected truncation radius for typical T Tauri disks. As a result, their current orbital locations require an explanation beyond standard disk migration or in situ formation. Modern theories of planet–disk interactions indicate that once a planet migrates close to the disk’s inner truncation radius, Type I torques vanish or switch direction, depending on the stellar and disk conditions, so that the planet is expected to stop its orbital decay and become trapped. In this work, we show that that magnetically driven sub-Keplerian gas flow in the inner disk can naturally counteract these effects and produce systems with USP planets at their observed orbital radii. The sub-Keplerian gas flow provides a headwind to small planets, and the resulting torque can overcome the effects of outward Type I migration near the corotation radius. For suitable disk and planet parameters, the torques due to the sub-Keplerian gas flow lead to inward migration on a rapid timescale. Over the time span of an FU Ori outburst, which moves the disk truncation radius inward, the rapid headwind migration can place planets in USP orbits. The combination of headwind migration and FU Ori outbursts thus provides a plausible mechanism to move small planets from a = 0.05–0.1 au down to a = 0.01–0.02 au. This effect is amplified for low-mass planets, consistent with existing observations.