Trans-Neptunian Object dynamics even better explained by a stellar flyby after 4.5 Gyr of evolution
Abstract
The Trans-Neptunian objects (TNOs) formed together with the planets from a flat disc of gas and dust but now orbit the Sun mostly on inclined, eccentric orbits. One explanation for the TNOs' orbits is a close flyby of another star. One with a mass of Mp =0.8 Msun at qp = 110 au and ip =70° fits the observations. However, such close encounters were more frequent when the Sun was young and still part of its birth cluster. Assuming that the flyby happened then, we use numerical N-body simulations to model how the TNOs' orbits changed due to interactions with the planets over the 4.56 Gyr since the Sun formed. We find that the cold Kuiper belt region lost about 80% and the hot Kuiper belt population about 40% of its initial population. About 7% --8% of the TNOs were injected into the planet region, but almost all (99%) were ejected afterwards. By contrast, the orbital parameters of distant Sedna-like objects (q >60 au) remained basically unchanged. Surprisingly, in sum, these changes improve the fit to the observed TNO population even more, strengthening the argument for a close flyby to the Solar System. The remaining differences concern the location of the cold population and the inclination distribution of the Sedna population. We discuss possible reasons and steps to resolve these issues.
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BibTeX
@misc{pfalzner2026transneptunian,
title = {{Trans-Neptunian Object dynamics even better explained by a stellar flyby after 4.5 Gyr of evolution}},
author = {Susanne Pfalzner and Frank W. Wagner and Marco Bischoff},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03575},
eprint = {2609.03575},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03575},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Trans-Neptunian Object dynamics even better explained by a stellar flyby after 4.5 Gyr of evolution
AU - Susanne Pfalzner
AU - Frank W. Wagner
AU - Marco Bischoff
PY - 2026
DA - 2026/09/03
PB - arXiv
DO - 10.48550/arxiv.2609.03575
UR - https://arxiv.org/abs/2609.03575
AB - The Trans-Neptunian objects (TNOs) formed together with the planets from a flat disc of gas and dust but now orbit the Sun mostly on inclined, eccentric orbits. One explanation for the TNOs' orbits is a close flyby of another star. One with a mass of M_p =0.8 Msun at q_p = 110 au and i_p =70° fits the observations. However, such close encounters were more frequent when the Sun was young and still part of its birth cluster. Assuming that the flyby happened then, we use numerical N-body simulations to model how the TNOs' orbits changed due to interactions with the planets over the 4.56 Gyr since the Sun formed. We find that the cold Kuiper belt region lost about 80% and the hot Kuiper belt population about 40% of its initial population. About 7% --8% of the TNOs were injected into the planet region, but almost all (99%) were ejected afterwards. By contrast, the orbital parameters of distant Sedna-like objects (q >60 au) remained basically unchanged. Surprisingly, in sum, these changes improve the fit to the observed TNO population even more, strengthening the argument for a close flyby to the Solar System. The remaining differences concern the location of the cold population and the inclination distribution of the Sedna population. We discuss possible reasons and steps to resolve these issues.
ER -