No evidence for interstellar planetesimals trapped in the Solar system

A Morbidelli,R Brasser,S N Raymond,K Batygin

doi:10.1093/mnrasl/slaa111

Abstract

ABSTRACT In two recent papers published in MNRAS, Namouni and Morais claimed evidence for the interstellar origin of some small Solar system bodies, including: (i) objects in retrograde co-orbital motion with the giant planets and (ii) the highly inclined Centaurs. Here, we discuss the flaws of those papers that invalidate the authors’ conclusions. Numerical simulations backwards in time are not representative of the past evolution of real bodies. Instead, these simulations are only useful as a means to quantify the short dynamical lifetime of the considered bodies and the fast decay of their population. In light of this fast decay, if the observed bodies were the survivors of populations of objects captured from interstellar space in the early Solar system, these populations should have been implausibly large (e.g. about 10 times the current main asteroid belt population for the retrograde co-orbital of Jupiter). More likely, the observed objects are just transient members of a population that is maintained in quasi-steady state by a continuous flux of objects from some parent reservoir in the distant Solar system. We identify in the Halley-type comets and the Oort cloud the most likely sources of retrograde co-orbitals and highly inclined Centaurs.

Highlights

The passages of the interstellar objects 1I/Oumuamua and 2I/Borisov through the Solar system on clearly hyperbolic orbits have stimulated interest in extrasolar planetesimals and their similarities and differences with the small bodies of the Solar system
It is not surprising that the claims by Namouni & Morais (2018, 2020) on the existence of populations of extrasolar planetesimals stranded in the Solar system since 4.5 Gy ago have attracted some attention in the astronomical community and in the media
The logic of the presented arguments suffers from significant drawbacks, and the methods are unsupported by modern knowledge of the behaviour of chaotic dynamical systems

Summary

INTRODUCTION

The passages of the interstellar objects 1I/Oumuamua and 2I/Borisov through the Solar system on clearly hyperbolic orbits have stimulated interest in extrasolar planetesimals and their similarities and differences with the small bodies of the Solar system. It is not surprising that the claims by Namouni & Morais (2018, 2020) on the existence of populations of extrasolar planetesimals stranded in the Solar system since 4.5 Gy ago have attracted some attention in the astronomical community and in the media. The willingness of Namouni and Morais to consider unconventional possibilities is admirable, the analyses outlined in the aforementioned papers are not correct. We summarize the main steps of the Namouni and Morais analysis, and discuss why they are not valid

A BRIEF SUMMARY OF THE WORK BY NAMOUNI AND MORAIS

T H E FATA L F L AW S

CONCLUSION