A unitary model for the formation of terrestrial planets and (rocky) close-in super-Earths

Tuesday 3 July, 12:20

We study the growth of rocky planets by pebble accretion in a protoplanetary disk. We find that the process is sensitively dependent on the pebble mass-flux. If the flux is small, planetary embryos grow slowly and remain low-mass. Hence their migration in the disk is negligible and their remain throughout the disk. At the disappearance of the gas, the embryos naturally become unstable and a smaller number of planets are formed by mutual collisions. This evolution is analog to that described for the formation of the Solar System terrestrial planets. We find that the largest mass of the planetary embryos is about 3 Mars-mass and the final mass of the final terrestrial planets is at most 3-4 Earth masses.  

If the pebble mass-flux is higher, the embryos grow faster and become more massive. Their migration in the disk becomes relevant. The accumulation of the embryos towards the inner edge of the disk leads to the formation of more massive objects by mutual merging. Larger masses enhance the migration and the pebble accretion rate. This leads to the formation of a system of close-in super-Earths, with masses up to 10 Earth masses. Instabilities of these super-Earth systems after the disappearance of the disk, lead to additional merging events.

We find that a change of less than a factor of 2 in the pebble flux can be enough to change the evolution from the terrestrial planet to the super-Earth growth modes.

Co-authors: M.Lambrechts, S.Jacobson, A.Johansen, A.Izidoro, S.Raymond, B.Bitsch

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