Shaken, not stirred: inefficient mixing of CM- and CI-like materials

Abstract

A recent study suggests that CM chondrite-like planetesimals formed in the vicinity of Saturn, in a pressure bump outside the gap carved by proto-Jupiter. While a fraction of these objects was implanted into the asteroid belt as a consequence of Saturn's growth, it remains unclear whether the scattered remainder could reach the ice-giant region and mix with more distant carbonaceous reservoirs. We test whether outward scattering during Saturn's growth and migration can implant CM-like bodies onto long-lived orbits in the Uranus-Neptune region, where they could contaminate the CI reservoir. We performed N-body integrations of 100 km planetesimals launched from the outer edge of Jupiter's gap, including gas drag and the gravitational perturbations of growing Jupiter and Saturn, with optional inclusion of a nearby ice-giant embryo. We explored a range of gas surface-density profiles and growth timescales. While Saturn's growth efficiently scatters CM-like planetesimals, fewer than about 2 percent are implanted beyond 15 au, even under gas-rich conditions, because gas drag damps their eccentricities and drives them back toward their perihelia rather than allowing them to circularize at larger distances. Adding an ice-giant core modestly increases the outward reach (up to about 4 percent in the most gas-rich case), but Type-I migration further lowers perihelia, making long-term retention at large distances difficult. For a CM mass budget M_CM,tot about 1 M_Earth, this implies at most M_CM < 0.02-0.04 M_Earth reaches 15-25 au, corresponding to a diluted mass fraction < (1-2) x 10^-3 in the outer ring, hence negligible contamination of the CI reservoir. Combined with the distinct radial distributions of CM- and CI-like asteroids in the belt, these results imply limited mixing of carbonaceous reservoirs and isolation of the CI reservoir.

References in corpus (18)

• Origin of the Structure of the Kuiper Belt during a Dynamical Instability in the Orbits of Uranus and Neptune
• Separating gas-giant and ice-giant planets by halting pebble accretion
• The structure of protoplanetary discs around evolving young stars
• Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion
• Three-dimensional simulations of multiple protoplanets embedded in a protostellar disc
• Planetesimal rings as the cause of the Solar System's planetary architecture
• The Formation of the Oort Cloud in Open Cluster Environments
• Dynamical evidence for an early giant planet instability
• Constraining the giant planets' initial configuration from their evolution: implications for the timing of the planetary instability
• Connecting Asteroids and Meteorites with visible and near-infrared spectroscopy
• The Formation of Uranus & Neptune: Challenges and Implications For Intermediate-Mass Exoplanets
• Origin of isotopic diversity among carbonaceous chondrites
• Source regions of carbonaceous meteorites and NEOs
• Runaway gas accretion and gap opening versus type~I migration
• Eccentricity excitation and merging of planetary embryos heated by pebble accretion
• The Ni isotopic composition of Ryugu reveals a common accretion region for carbonaceous chondrites
• Sequential giant planet formation initiated by disc substructure
• On the interaction of pebble accreting embryos with the gaseous disc: importance of thermal forces