Evidence for very early migration of the Solar System planets from the Patroclus–Menoetius binary Jupiter Trojan

Abstract

The orbital distribution of trans-Neptunian objects provides strong evidence for the radial migration of Neptune [1,2]. The outer planets' orbits are thought to have become unstable during the early stages [3] with Jupiter having scattering encounters with a Neptune-class planet [4]. As a consequence, Jupiter jumped inward by a fraction of an au, as required from inner solar system constraints [5,6], and obtained its current orbital eccentricity. The timing of these events is often linked to the lunar Late Heavy Bombardment that ended ∼700 Myr after the dispersal of the protosolar nebula (t 0 ) [7,8]. Here we show instead that planetary migration started shortly after t 0 . Such early migration is inferred from the survival of the Patroclus-Menoetius binary Jupiter Trojan [9]. The binary formed at t t 0 [10,11] within a massive planetesimal disk once located beyond Neptune [12,13]. The longer the binary stayed in the disk, the greater the likelihood that collisions would strip its components from one another. The simulations of its survival indicate that the disk had to have been dispersed by migrating planets within 100 Myr of t 0 . This constraint implies that the planetary migration is unrelated to the formation of the youngest lunar basins.Jupiter Trojans (JTs) are a population of small bodies with orbits near Jupiter [14].They hug two equilibrium points of the three-body problem, known as L 4 and L 5 , with semimajor axes a ≃ 5.2 au, eccentricities e < 0.15, and inclinations i < 40 • . Dynamical models suggest that JTs formed in the outer planetesimal disk between ∼20 au and 30 au and were implanted onto their present orbits after having a series of scattering encounters with the outer planets [12,13]. This resolves a long-standing conflict between the previous formation theories that implied i < 10 • and high orbital inclinations of JTs. The formation

Binary survival in the outer solar system

“…Myr; see also Nesvorný et al 2018). The disk could have started with a rounded size distribution of planetesimals, as indicated by the streaming instability simulations 5.…”

“…Binaries with smaller (larger) components have lower (higher) survival chances, as already noted inNesvorný et al (2011) andParker et al (2012). The implications of these results for the binary occurrence in the Kuiper belt are discussed in Section 6.Motivated by the results ofNesvorný et al (2018), we now consider t disk < 100 Myr(Figures…”

“…Here we study the effects of planetary encounters on binaries starting in the massive disk below ∼30 au and reaching orbits in the hot population (i.e., HCs, resonant and scattered objects). This scientific problem was not considered before (see Noll et al 2006 andNesvorný et al 2018 for related studies of Centaurs and Jupiter Trojans) at least partly because we did not have a reliable model for the implantation of objects in the Kuiper belt. Here we use the implantation model of , which has a long heritage in the previous works on the subject (e.g., Hahn & Malhotra 2005, Levison et al 2008.…”

Realistic On-the-fly Outcomes of Planetary Collisions. II. Bringing Machine Learning to N-body Simulations

“…Morbidelli et al (2018) found that the abundances of highly siderophile elements in the lunar mantle can be explained by the accretion tail from the formation of the terrestrial planets. The presence of binary Jupiter trojans has also been interpreted as an evidence for a very early migration (Nesvorný et al 2018). Both these studies favor an early instability, if it ever took place.…”

Very Slow Rotators from Tidally Synchronized Binaries

“…If the disk was long-lived (e.g., t disk ∼ 100 Myr), more binaries would become unbound by impacts. Binaries were also dissociated by dynamical perturbations during planetary encounters that occurred as bodies evolved from ∼20-30 au to 5.2 au (Nesvorný et al 2018, Nesvorný & Vokrouhlický 2019. 1 We ignore the effect of tides on binary semimajor axis.…”