A reassessment of the in situ formation of close-in super-Earths

Abstract

A large fraction of stars host one or multiple close-in super-Earth planets. There is an active debate about whether these planets formed in situ or at greater distances from the central star and migrated to their current position. It has been shown that part of their observed properties (e.g., eccentricity distribution) can be reproduced by N-body simulations of in situ formation starting with a population of protoplanets of high masses and neglecting the effects of the disk gas. We plan to reassess the in situ formation of close-in super-Earths through more complete simulations. We performed N-body simulations of a population of small planetary embryos and planetesimals that include the effects of disk-planet interactions (e.g., eccentricity damping, type I migration). In addition, we also consider the accretion of a primitive atmosphere from a protoplanetary disk. We find that planetary embryos grow very quickly well before the gas dispersal, and thus undergo rapid inward migration, which means that one cannot neglect the effects of a gas disk when considering the in-situ formation of close-in super-Earths. Owing to their rapid inward migration, super-Earths reach a compact configuration near the disk's inner edge whose distribution of orbital parameters matches the observed close-in super-Earths population poorly. On the other hand, simulations including eccentricity damping, but no type I migration, reproduce the observed distributions better. Including the accretion of an atmosphere does not help reproduce the bulk architecture of observations. Interestingly, we find that the massive embryos can migrate inside the disk edge while capturing only a moderately massive hydrogen/helium atmosphere. By this process they avoid becoming giant planets. The bulk of close-in super-Earths cannot form in situ, unless type I migration is suppressed in the entire disk inside 1 AU.

9 pages, 7 figures, accepted for publication in A&A

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Cited by in corpus (10)

• Formation of planetary systems by pebble accretion and migration: How the radial pebble flux determines a terrestrial-planet or super-Earth growth mode
• Challenges in Planet Formation
• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• An Analytic Criterion for Turbulent Disruption of Planetary Resonances
• Formation of Close-in Super-Earths by Giant Impacts: Effects of Initial Eccentricities and Inclinations of Protoplanets
• Close-in Super-Earths: The first and the last stages of planet formation in an MRI-accreting disc
• Terrestrial Planets Formation under Migration: the Systems near 4:2:1 Mean Motion Resonance
• Dynamical rearrangement of super-Earths during disk dispersal II. Assessment of the magnetospheric rebound model for planet formation scenarios
• Building protoplanetary disks from the molecular cloud: redefining the disk timeline
• The potential of combining MATISSE and ALMA observations: Constraining the structure of the innermost region in protoplanetary discs