The Role of Early Giant Planet Instability in the Terrestrial Planet Formation


The Mars mass (MMars) and excitation of Venus/Earth orbits (he, ii) obtained in our 10-simulation sets. See caption of Fig. 12 for the description of different symbols. The circle marks the real values: MMars = 0.107 MEarth and he, ii = 0.0274 au. The dashed lines demarcate the region where MMars and he, ii are within a factor of two to the real values.

The terrestrial planets are believed to have formed by violent collisions of tens of lunar- to Mars-size protoplanets at time t<200 Myr after the protoplanetary gas disk dispersal (t_0).

The solar system giant planets rapidly formed during the protoplanetary disk stage and, after t_0, radially migrated by interacting with outer disk planetesimals. An early (t<100 Myr) dynamical instability is thought to have occurred with Jupiter having gravitational encounters with a planetary-size body, jumping inward by ~0.2-0.5 au, and landing on its current, mildly eccentric orbit. Here we investigate how the giant planet instability affected formation of the terrestrial planets. We study several instability cases that were previously shown to match many solar system constraints. We find that resonances with the giant planets help to remove solids available for accretion near ~1.5 au, thus stalling the growth of Mars.

It does not matter, however, whether the giant planets are placed on their current orbits at t_0 or whether they realistically evolve in one of our instability models; the results are practically the same. The tight orbital spacing of Venus and Earth is difficult to reproduce in our simulations, including cases where bodies grow from a narrow annulus at 0.7-1 au, because protoplanets tend to radially spread during accretion. The best results are obtained in the narrow-annulus model when protoplanets emerging from the dispersing gas nebula are assumed to have (at least) the Mars mass. This suggests efficient accretion of the terrestrial protoplanets during the first ~10 Myr of the solar system.

David Nesvorny, Fernando V. Roig, Rogerio Deienno
Comments: AJ, in press
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2012.02323 [astro-ph.EP] (or arXiv:2012.02323v1 [astro-ph.EP] for this version)
Submission history
From: David Nesvorny
[v1] Thu, 3 Dec 2020 23:12:02 UTC (320 KB)
https://arxiv.org/abs/2012.02323

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