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Radial Distribution of Distant Trans-Neptunian Objects Points to Sun’s Formation in a Stellar Cluster

Presentation #209.06 in the session TNO Theory/Formation and Observational Surveys (Oral Presentation)

Published onOct 23, 2023
Radial Distribution of Distant Trans-Neptunian Objects Points to Sun’s Formation in a Stellar Cluster

The Scattered Disk Objects (SDOs) are a population of trans-Neptunian bodies with semimajor axes 50<a<1000 au and perihelion distances q > 30 au. The detached SDOs with orbits beyond the reach of Neptune (roughly q>35 au) are of special interest in this work as an important constraint on the early evolution of the outer Solar System. The semimajor axis profile of detached SDOs at 50-500 au, as characterized from the Dark Energy Survey (DES), is radially extended, but previous dynamical models of Neptune’s early migration produce a relatively compact profile. This problem is most likely related to Sun’s birth environment in a stellar cluster. We perform new dynamical simulations that account for cluster effects and show that the orbital distribution of SDOs can be explained if a particularly close stellar encounter occurred early on (e.g., M dwarf with the mass ~0.2 MSun approaching the Sun at ~200 au). For such an encounter to happen with a reasonably high probability the Sun must have formed in a stellar cluster with eta T ≳ 104 Myr pc-3, where eta is the stellar number density and T is the Sun’s residence time in the cluster.

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