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Explaining the giant planet formation around late-M dwarfs

Presentation #615.02 in the session Planet Formation Theory.

Published onApr 03, 2024
Explaining the giant planet formation around late-M dwarfs

Late M dwarfs are the end tail of low-mass stars with a typical stellar mass of 0.1−0.2 M. The occurrence rate of giant planets with a mass higher than 30 M has been observed to correlate with stellar mass. Despite the intrinsically low occurrence rate, a few giant planets have been discovered around late dwarfs. While with the current core accretion model, it is difficult to reproduce the observed giant planet population around very-low-mass stars. In pebble accretion, the core masses of the planets are limited by the pebble isolation mass. Here we propose a hybrid growth model that utilizes both pebble accretion and planet-planet collisions to explain the giant planet formation and search for the formation zone. In this scenario, the planetary cores can exceed the pebble isolation mass barrier aided by frequent planet-planet collisions. This consequently speeds up their gas accretion and promotes giant planet formation. Massive planets are more likely to form in disks with longer lifetimes, higher solid masses, moderate to high levels of disk turbulence, and larger initial masses of protoplanets. Around very low-mass stellar hosts, the giant planets are still likely to form when lunar-mass protoplanets first emerge from planetesimal accretion and then grow rapidly by a combination of pebble accretion and planet-planet collisions in disks with a high supply of pebble reservoir > 50 M and turbulent level of αt ~ 10-3-10-2.

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