Survivor bias: divergent fates of the Solar System's ejected vs. persisting planetesimals

TL;DR

This study uses N-body simulations to compare the dynamical pathways and physical fates of ejected versus surviving planetesimals in the Solar System, revealing higher disruption and volatile loss rates among ejected objects.

Contribution

It provides a detailed analysis of the divergent dynamical and physical evolution of planetesimals based on their fates, incorporating thermal evolution effects of giant planets.

Findings

Ejected planetesimals have over twice the tidal disruption rate of surviving ones.

Disruption is mainly caused by Jupiter for ejected objects and Neptune for survivors.

Ejected objects show greater diversity in physical properties, aligning with observations of interstellar objects.

Abstract

The orbital architecture of the Solar System is thought to have been sculpted by a dynamical instability among the giant planets. During the instability a primordial outer disk of planetesimals was destabilized and ended up on planet-crossing orbits. Most planetesimals were ejected into interstellar space but a fraction were trapped on stable orbits in the Kuiper belt and Oort cloud. We use a suite of N-body simulations to map out the diversity of planetesimals' dynamical pathways. We focus on two processes: tidal disruption from very close encounters with a giant planet, and loss of surface volatiles from repeated passages close to the Sun. We show that the rate of tidal disruption is more than a factor of two higher for ejected planetesimals than for surviving objects in the Kuiper belt or Oort cloud. Ejected planetesimals are preferentially disrupted by Jupiter and surviving ones by Neptune. Given that the gas giants contracted significantly as they cooled but the ice giants did not, taking into account the thermal evolution of the giant planets decreases the disruption rate of ejected planetesimals. The frequency of volatile loss and extinction is far higher for ejected planetesimals than for surviving ones and is not affected by the giant planets' contraction. Even if all interstellar objects were ejected from Solar System-like systems, our analysis suggests that their physical properties should be more diverse than those of Solar System small bodies as a result of their divergent dynamical histories. This is consistent with the characteristics of the two currently-known interstellar objects.