Distinct origins for CM and CI-like bodies: Saturn formation region versus trans-Neptunian disk

Abstract

To date, the vast majority of meteorites (≥99%) originate from asteroids in orbits between Mars and Jupiter, yet reaching a consensus on how their diverse chemical, compositional, and isotopic characteristics align with an in-situ formation model within the asteroid belt remains elusive. Recent dynamical models, leveraging measurements from carbonaceous chondrites (CCs), suggest that meteorites may originate from varied heliocentric distances, spanning from the terrestrial planet formation zone to the Kuiper Belt [1, 2, 3]. This broad range is evident in the distribution dichotomies among CCs, especially between CM chondrites (Ch, Cgh-types) and CI chondrites (B, C, Cb, and Cg-types), which collectively account for over 50% of the asteroid belt's mass, excluding Ceres  [4, 5, 6]. These groups show distinctly different spatial distributions (Fig. 1): CM-like bodies display a Gaussian profile, whereas CI-like bodies show an asymmetric distribution, similar to comet-like P-type asteroids [7]. Our study aims to explore the formation and migration history of these asteroid types within the context of giant planet evolution and solar system dynamics to determine whether CM and CI chondrites originated from different locations or at different times.

We use an orbital model initially developed by Ronnet et al. (2018) [8] to investigate the injection of planetesimals into the asteroid belt following giant planet growth in the protoplanetary disk (PSD). We conduct simulations using REBOUND, consisting of 20,000 test particles each, representing 100-km-sized planetesimals. Our five-planet model, inspired by the works of Nesvorný et al. (2015) [9] and Dienno et al. (2017) [10], features Jupiter, Saturn, an additional ice giant (commonly ejected from the solar system), Uranus, and Neptune. Initially, planets are located on low-eccentricity orbits, with Jupiter at 5.4 au and Saturn at the edge of its gap, at 7.3 au. We choose to neglect the influence of the telluric planets, which, having relatively small orbits, require more computation time. We place Neptune in two different configurations: a 'tight' configuration at 16.2 au, in a 3:2, 3:2, 3:2, 3:2 resonance chain, and a 'wide' configuration at 20.3 au, in a 3:2, 3:2, 2:1, 3:2 resonance chain. The test particles' semi-major axes are initialized uniformly between 7 au and 1 au beyond the orbit of Neptune. We examine the effects of gas profile (Σg), planetary growth timescale (τgrowth), and the viscosity parameter (α) on the distribution of planetesimals implanted in the asteroid belt. Notably, we investigate three different gas profiles: the traditional canonical model with a radial dependency of Σg ∝ r−0.5 [11], the Desch et al. 2018 model [12], and the Raymond & Izidoro 2017 model [3].

This study's findings aim to contribute significantly to our understanding of the dynamic processes that shaped the early solar system and the specific pathways that led to the observed dichotomy—or trichotomy—in carbonaceous chondrite composition. By comparing the outcomes of our simulations with existing data, we anticipate providing new insights into the ongoing debate over the formational contexts of these asteroids, thereby enhancing the broader astrophysical models concerning planetary formation and migration.

Figure 1: Distinct spectral classifications (CM, CI/IDP, S) reveal systematic differences in the distributions of main-belt asteroids with D>100 km.

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