Shape models and spin states of Jupiter Trojans

Testing the streaming instability formation scenario^★

¹ Charles University, Faculty of Mathematics and Physics, Institute of Astronomy, V Holešovičkách 2, 18000 Prague 8, Czech Republic
e-mail: josef.hanus@mff.cuni.cz
² Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA
³ Center for Solar System Studies, 9302 Pittsburgh Ave. Suite 200, Rancho Cucamonga, CA 91730, USA
⁴ Belgrade Astronomical Observatory, Volgina 7, 11060 Belgrade 38, Serbia
⁵ Blue Mountains Observatory, Leura, Australia
⁶ Department of Physics, The Catholic University of America, Washington, DC 20064, USA
⁷ Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁸ Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD 20771, USA

Received: 30 January 2023
Accepted: 26 June 2023

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°) 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.