Shape models and spin states of Jupiter Trojans: Testing the streaming instability formation scenario

TL;DR

This study analyzes the shapes and spin states of approximately 1000 Jupiter Trojans to test if their properties align with formation via streaming instability in the trans-Neptunian disk, finding broad consistency with some discrepancies explained by collisional effects.

Contribution

The paper provides the first comprehensive shape and spin state analysis of a large Jupiter Trojan sample, testing formation theories through observational data and simulations.

Findings

Pole obliquity distribution broadly matches streaming instability predictions.

Some asymmetry in prograde vs. retrograde poles can be explained by collisional activity.

Post-capture spin evolution has minimal impact on pole distribution.

Abstract

The leading theory for the origin of Jupiter Trojans (JTs) assumes that JTs were captured to their orbits near the Lagrangian points of Jupiter during the early reconfiguration of the giant planets. The natural source region for the majority of JTs would then be the population of planetesimals born in a massive trans-Neptunian disk. If true, JTs represent the most accessible stable population of small Solar System bodies that formed in the outer regions of the Solar System. For this work, we compiled photometric datasets for about 1000 JTs and applied the convex inversion technique in order to assess their shapes and spin states. We obtained full solutions for $79$ JTs, and partial solutions for an additional $31$ JTs. We found that the observed distribution of the pole obliquities of JTs is broadly consistent with expectations from the streaming instability, which is the leading mechanism for the formation of planetesimals in the trans-Neptunian disk. The observed JTs' pole distribution has a slightly smaller prograde vs. retrograde asymmetry (excess of obliquities $>130^\circ$) than what is expected from the existing streaming instability simulations. However, this discrepancy can be plausibly reconciled by the effects of the post-formation collisional activity. Our numerical simulations of the post-capture spin evolution indicate that the JTs' pole distribution is not significantly affected by dynamical processes such as the eccentricity excitation in resonances, close encounters with planets, or the effects of nongravitational forces. However, a few JTs exhibit large latitude variations of the rotation pole and may even temporarily transition between prograde- and retrograde-rotating categories.