Shaving the Outskirts of Planetary Systems Probed by Roman via Stellar Flybys
Abstract
The recently launched Nancy Grace Roman Space Telescope (\textit{Roman}) will soon begin observations that promise to revolutionize our understanding of exoplanet demographics. \textit{Roman}'s Galactic Bulge Time-Domain Survey (GBTDS) will observe the Galactic Bulge via transit and microlensing techniques, providing a unique opportunity to study hot Jupiters as well as long-period/free-floating exoplanets in a dense and kinematically hot stellar environment. In this Letter, we quantify how repeated, impulsive stellar flybys truncate the outskirts of planetary systems in the Bulge. We find that flybys result in ejections on ∼Gyr timescales for wide orbits (≳ 250 au) around low-mass hosts. Provided these wide orbits are populated, these ejections likely contribute to the population of free-floating planets probed by \textit{Roman}. Surviving planets outside of ∼ 10 au are placed on eccentric and misaligned orbits. We show that, though systems suffer many close encounters, the evolution is dominated by the single strongest perturbation; planetary orbits (even those that evade ejection) undergo superdiffusion (i.e. a Lévy flight). We comment on the implications of our results for the origin of hot Jupiters amenable to Roman's transit search. Our work serves as a quantitative baseline from which future dynamical studies can build to better understand the evolution of planetary systems in the Galactic Bulge.
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BibTeX
@misc{liveoak2026shaving,
title = {{Shaving the Outskirts of Planetary Systems Probed by Roman via Stellar Flybys}},
author = {Donald Liveoak and Tim Hallatt and Sarah Millholland},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.06112},
eprint = {2609.06112},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.06112},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Shaving the Outskirts of Planetary Systems Probed by Roman via Stellar Flybys
AU - Donald Liveoak
AU - Tim Hallatt
AU - Sarah Millholland
PY - 2026
DA - 2026/09/05
PB - arXiv
DO - 10.48550/arxiv.2609.06112
UR - https://arxiv.org/abs/2609.06112
AB - The recently launched Nancy Grace Roman Space Telescope (\textit{Roman}) will soon begin observations that promise to revolutionize our understanding of exoplanet demographics. \textit{Roman}'s Galactic Bulge Time-Domain Survey (GBTDS) will observe the Galactic Bulge via transit and microlensing techniques, providing a unique opportunity to study hot Jupiters as well as long-period/free-floating exoplanets in a dense and kinematically hot stellar environment. In this Letter, we quantify how repeated, impulsive stellar flybys truncate the outskirts of planetary systems in the Bulge. We find that flybys result in ejections on ∼Gyr timescales for wide orbits (≳ 250 au) around low-mass hosts. Provided these wide orbits are populated, these ejections likely contribute to the population of free-floating planets probed by \textit{Roman}. Surviving planets outside of ∼ 10 au are placed on eccentric and misaligned orbits. We show that, though systems suffer many close encounters, the evolution is dominated by the single strongest perturbation; planetary orbits (even those that evade ejection) undergo superdiffusion (i.e. a Lévy flight). We comment on the implications of our results for the origin of hot Jupiters amenable to Roman's transit search. Our work serves as a quantitative baseline from which future dynamical studies can build to better understand the evolution of planetary systems in the Galactic Bulge.
ER -