Abstract

Asteroids and comets - being relics of the early Solar System stages - are fundamental to our understanding of its formation and history ; and possibly for the origin of life as a source of water and organic material delivery onto our primitive Earth. One still intriguing source of long period comets with large eccentricities and inclinations, is the hypothetical Oort cloud. Such objects can be triggered to move in the inner Solar System region as well as being ejected to interstellar space ; similarly inter-stellar objects originating from other stars have also visited our Solar System. This outer region being the interface of the Solar System dynamics with the stellar environment and the galactic potential, it tackles different domains of astronomy. All having moreover shown recent development thanks to the results of recent European Gaia mission data release and show potential with the future Gaia releases, LSST and other survey programmes, and the Comet Interceptor mission.

We have build up an ISSI international team to work on this topic ;
https://teams.issibern.ch/outermostsolarsystem/
and will have our kick off meeting in Paris. Two other team meeting will be held at ISSI Bern.

Scientific justification

Small Solar System bodies well beyond Neptune – from Trans-Neptunian Objects (TNOs) up to the Oort cloud objects – lie at the interface of the Sun’s sphere of influence and its interstellar environment. Their dynamics is shaped by the gravitational influence of both our Solar System and the stellar and galactic environment in which it evolved over time. Besides, being the most pristine objects, they are tracers of the formation and the dynamical evolution of the outermost part of the Solar System. Indeed, their dynamics is structured by these complex mix of interactions from the inside by the giant planets and on the outside by stellar encounters, and the galactic potential along the orbital evolution of the whole Solar System in the Milky Way.

We aim to understand how planetary and stellar interactions have shaped the Outermost Solar System since its formation some 4.5 Gyr ago. Our approach is based on combining the knowledge gained by observational advances on the populations of TNOs and comets (mostly from recent surveys and the soon-to-start Rubin/LSST), together with a state-of-art knowledge and modelling of the local stellar and galactic environment (much of which has come from the Gaia mission). We will develop dedicated numerical N-body simulations, taking into account all relevant gravitational interactions, and comparing the outputs to observed orbital distributions of these small bodies. By bringing together world-experts on galactic dynamics, stellar populations, Solar System dynamics and observations, we provide the ideal conditions to achieve a deeperunderstanding of the environment in which the Solar System has evolved, and test models for the formation of the Oort cloud.

By using computational tools and observational datasets, there are several general questions we will address in this collaborative work :
• What is the influence of the stellar and galactic environment ? What are the characteristics of the Sun’s birth stellar cluster ? What influence did the environment, galactic structure and galactic potential have since then ? What are the details of recent and future individual stellar close encounters ?
• What are the observational constraints given by the small bodies ? What is the influence of planetary perturbations at the early stages ? What is the origin and distribution of extreme TNOs (sednoids and other high-perihelion objects) ? What is the mass ratio between the scattered disc and the Oort cloud ?

Preliminary scientific program

. Stellar and Galactic environment
. Outer Solar System up to the Oort cloud, and Inter-Stellar Objects
. Surveys deciphering Physical and Dynamical properties of Small Solar System Bodies

Arika Higuchi Kyoto Sangyo University, JAPAN
Coryn Bailer-Jones MPIA Heidelberg, GERMANY
Daniel Hestroffer (coord) LTE/Paris observatory, FRANCE
Elke Pilat-Lohinger TU Graz, AUSTRIA
Luke Dones SWRI Boulder,USA
Marc Fouchard Université de Lille, FRANCE
Merce Romero-Gómez ICCUB Barcelona, SPAIN
Paola DiMatteo LIRA/Paris observatory, FRANCE
Paul McMillan Leicester University, UK
Pedro Bernardinelli DiRAC/UW, USA
Susanne Pfalzner FZ Jülich, GERMANY
Takashi Ito CfCA/NAOJ, Tokyo JAPAN

Alexandre Bougakov (PhD) Paris observatory, FRANCE
Frank Wagner (post-doc) FZ Jülich, GERMANY
Josefa Grossschedl (post-doc) Acad. Science Prague, CZECHIA
Maximilian Zimmermann (PhD) University of Wien, AUSTRIA
Rosita Kokotanekova ISSI Bern
Misha Haywood Paris observatory
Rosine Lallement Paris observatory
Tristan Boin Paris observatory
Ziyu Liu Paris observatory
Jean Souchay Paris observatory