The great dichotomy of the Solar System: Small terrestrial embryos and massive giant planet cores

By A. Morbidelli, Michiel Lambrechts, Seth Andrew Jacobson, B. Bitsch. 2015

176 citations recorded by the source corpus.

The basic structure of the Solar System is set by the presence of low-mass terrestrial planets in its inner part and giant planets in its outer part. This is the result of the formation of a system of multiple embryos with approximately the mass of Mars in the inner disk and of a few multi-Earth-mass cores in the outer disk, within the lifetime of the gaseous component of the protoplanetary disk. What was the origin of this dichotomy in the mass distribution of embryos/cores? We show in this paper that the classic processes of runaway and oligarchic growth from a disk of planetesimals cannot explain this dichotomy, even if the original surface density of solids increased at the snowline. Instead, the accretion of drifting pebbles by embryos and cores can explain the dichotomy, provided that some assumptions hold true. We propose that the mass-flow of pebbles is two-times lower and the characteristic size of the pebbles is approximately ten times smaller within the snowline than beyond the snowline (respectively at heliocentric distance r r(ice) where r(ice) is the snowline heliocentric distance), due to ice sublimation and the splitting of icy pebbles into a collection of chondrule-size silicate grains. In this case, objects of original sub-lunar mass would grow at drastically different rates in the two regions of the disk. Within the snowline these bodies would reach approximately the mass of Mars while beyond the snowline they would grow to similar to 20 Earth masses. The results may change quantitatively with changes to the assumed parameters, but the establishment of a clear dichotomy in the mass distribution of protoplanets appears robust provided that there is enough turbulence in the disk to prevent the sedimentation of the silicate grains into a very thin layer. (C) 2015 Elsevier Inc. All rights reserved. (Less)

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/14753dcf08c0ec71b19f34ca5356f2fd70a33f6c

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Citations in the corpus

The nature of the TRAPPIST-1 exoplanets. (2018, background): “Models of pebble accretion find that large embryos preferentially grow beyond the snow line (Morbidelli et al. 2015; Ormel et al. 2017).”
Planetesimal formation near the snowline: in or out? (2017, background): “We assume that in the outer disk, half of the mass in pebbles consists of water ice, and the other half consists of silicates (Lodders 2003; Morbidelli et al. 2015).”
Planetesimal formation starts at the snow line (2017, methodology): “The great dichotomy of the Solar System used to be commonly attributed to the jump change of condition around the snow line (Stevenson & Lunine 1988; Wuchterl et al. 2000; Morbidelli et al. 2015), with water ice greatly enhancing the abundance of solids outside of this point.”
Breaking the chains: hot super-Earth systems from migration and disruption of compact resonant chains (2017, background): “Instead, the formation of massive objects beyond the snowline within the lifetime of the disc seems to be generic from theoretical considerations (e.g. Morbidelli et al. 2015).”
Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion (2017, background): “By the time of Jupiter’s gas accretion, the terrestrial region is thought to have been made up of roughly Mars-sized planetary embryos (Kokubo and Ida, 2000; Morbidelli et al., 2015) that presumably accreted predominantly from local, reduced material.”
Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants (2018, background): “This makes the accretion very efficient because larger pebbles can be accreted more efficiently, allowing Jupiter to grow faster than the bodies in the terrestrial region (Morbidelli et al. 2015).”
The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present (2016, background): “One explanation for this apparent contradiction is that the inward drift of water-rich bodies was blocked when Jupiter formed (Morbidelli et al. 2015).”