Building the terrestrial planets: Constrained accretion in the inner Solar System

By S. Raymond, D. O'Brien, A. Morbidelli, N. Kaib. 2009

372 citations recorded by the source corpus.

Abstract To date, no accretion model has succeeded in reproducing all observed constraints in the inner Solar System. These constraints include: (1) the orbits, in particular the small eccentricities, and (2) the masses of the terrestrial planets – Mars’ relatively small mass in particular has not been adequately reproduced in previous simulations; (3) the formation timescales of Earth and Mars, as interpreted from Hf/W isotopes; (4) the bulk structure of the asteroid belt, in particular the lack of an imprint of planetary embryo-sized objects; and (5) Earth’s relatively large water content, assuming that it was delivered in the form of water-rich primitive asteroidal material. Here we present results of 40 high-resolution ( N = 1000–2000) dynamical simulations of late-stage planetary accretion with the goal of reproducing these constraints, although neglecting the planet Mercury. We assume that Jupiter and Saturn are fully-formed at the start of each simulation, and test orbital configurations that are both consistent with and contrary to the “Nice model”. We find that a configuration with Jupiter and Saturn on circular orbits forms low-eccentricity terrestrial planets and a water-rich Earth on the correct timescale, but Mars’ mass is too large by a factor of 5–10 and embryos are often stranded in the asteroid belt. A configuration with Jupiter and Saturn in their current locations but with slightly higher initial eccentricities ( e = 0.07–0.1) produces a small Mars, an embryo-free asteroid belt, and a reasonable Earth analog but rarely allows water delivery to Earth. None of the configurations we tested reproduced all the observed constraints. Our simulations leave us with a problem: we can reasonably satisfy the observed constraints (except for Earth’s water) with a configuration of Jupiter and Saturn that is at best marginally consistent with models of the outer Solar System, as it does not allow for any outer planet migration after a few Myr. Alternately, giant planet configurations which are consistent with the Nice model fail to reproduce Mars’ small size.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/c0ffc4a5f271f0db133d9828e8a69b6cc0812ec8

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Citations in the corpus

Close-in planetesimal formation by pile-up of drifting pebbles (2016, background): “Raymond et al. (2009) show that it is impossible to reproduce the architecture of the inner solar system starting from an initially uniform distribution of planetesimals.”
Water delivery and giant impacts in the 'Grand Tack' scenario (2014, methodology): “This has typically been modeled as an idealized bimodal mass distribution of planetesimals and embryos, with approximately equal mass in each population (Chambers 2001; O’Brien et al. 2006; Raymond et al. 2009).”
The origins and concentrations of water, carbon, nitrogen and noble gases on Earth (2014, background): “the inner planet region : the locally dry bodies that were present in the Earth's forming region became depleted due to their accretion, which allowed more distant wet planetesimals to contribute to the proto-Earth as accretion proceeded (Morbidelli et al., 2000; Raymond et al., 2009; Walsh et al., ”
The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present (2016, background): “In the classical model of accretion, water-rich planetesimals originated in the outer asteroid belt (Morbidelli et al. 2000; Raymond et al. 2007a, 2009; Izidoro et al. 2015).”
Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion (2017, background): “…Petit et al., 2001; O’Brien et al., 2007), although in many simulations embryos survive after the terrestrial planets have formed, in conflict with the observed Solar System, as the imprint of embryos on surviving planetesimals would likely survive a Nice model instability (Raymond et al., 2009).”
Populating the asteroid belt from two parent source regions due to the migration of giant planets—“The Grand Tack” (2012, background): “However, models of terrestrial planet formation have consistently struggled to match the small mass of Mars relative to Earth (see Raymond et al. 2009).”
Building Terrestrial Planets (2012, background): “…originally had an orbit with an eccentricity comparable with or larger than the current one, little material would have been accreted from the outer asteroid belt, and the terrestrial planets would have been almost completely dry (O’Brien et al. 2006, Raymond et al. 2009), as noted in Section 5.4.”
A Perspective from Extinct Radionuclides on a Young Stellar Object: The Sun and Its Accretion Disk (2011, background): “However, dynamic simulations of terrestrial planet formation have difficulties explaining the small mass of Mars compared with the masses of Earth and Venus (Chambers & Cassen 2002, Raymond et al. 2009, Wetherill 1991).”
Formation of planetary systems by pebble accretion and migration (2018, background): “Their formation history is thus similar to the formation of the Earth through giant impacts (Chambers 2001; O’Brien et al. 2006; Raymond et al. 2009; Izidoro et al. 2014; Jacobson & Morbidelli 2014).”
The Origin of the Moon Within a Terrestrial Synestia (2018, background): “…different initial conditions and alternative configurations of the giant planets (e.g., Hansen, 2009; Levison et al., 2015; O’Brien et al., 2006; Raymond et al., 2009; Walsh et al., 2011) all produce high-energy impacts in the final stages of accretion although the frequency of different…”
Debris disks as signposts of terrestrial planet formation (2011, background): “This set is of particular interest because the surviving giant planets match the observed eccentricity distribution without any fine-tuning (Raymond et al. 2009a, 2010).”
The structure of protoplanetary discs around evolving young stars (2014, background): “The late stages of the disc evolution, where migration of newly formed gas giants shape the inner solar system (Raymond et al. 2009; Walsh et al. 2011) Even though these mechanisms happen on different length scales and time scales, they are all strongly dependent on the underlying disc structure…”