The outer solar system as consequence of a stellar flyby

• Applicant: Professorin Dr. Susanne Pfalzner
• Subject Area: Astrophysics and Astronomy
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450107816

The Solar System formed from a gas-dust disc with the consequence that the planets orbit nearly in a plane on close to circular orbits. During the last 20 years several thousand objects outside Neptune´s orbit were detected (transneptunian objects - TNOs). Surprisingly, most of them move on very eccentric and inclined orbits. The question is what leads to these unexpected orbits of the TNOs.The standard explanation assumes that the planets formed in an initially more compact configuration and that the TNOs are planetesimals that were scattered from their locations between the planets when the planets moved into their current positions. However, during the last few years, this theory lost some of its appeals as this model can, for example, not explain the existence of extreme TNOs like Sedna and did also not predict recently found new classes of TNOs. This calls for looking more into alternative scenarios.This project will investigate the scenario, where the close flyby of another star excited the TNOs to their current orbits. It is the central aim to test whether this scheme reproduces better the properties of the TNOs. The applicant performed a first "proof of principle study" where she demonstrated that such close flybys are reasonably common and give a qualitative match to the TNO population surpassing many problems that the scattering model has.The aim of this project is to advance from a qualitative to a quantitative description. This means finding the best-fit model in terms of the flyby parameters (mass, periastron distance and inclination of the perturber). When comparing the observation with the simulation results selection effects have to be taken into account as currently only of the fraction of the TNOs are actually detected. Besides, it will be taken into account that due to the interactions with Neptune the orbital parameters of the inner TNOs (30-45 AU) changed. These aspects will be considered and the long-term behaviour of TNOs investigated. With the advent of the LSST likely, thousands of new TNOs will be detected. It is the goal to make predictions for the distribution of these TNOs from the flyby scenario, which can then be directly tested.

• DFG Programme: Research Grants