Revealing the origin of desert dwellers via stellar obliquities
File(s)
Published version
Author(s)
Hallatt, Tim
Owen, James E
Millholland, Sarah
Type
Journal Article
Abstract
Observations suggest that the hot Neptune desert contains the remnants of destroyed gas giants. Recent theoretical work has shown that gas giant destruction via Roche lobe overflow (RLO) can indeed populate the desert with remnant planets, but only if mass transfer removes most of the planet’s orbital angular momentum (“lossy” RLO). Motivated by the fact that stellar accretion naturally gives rise to such lossy RLO, in this Letter we examine how planet-to-star mass and angular momentum transfer manifests in the distribution of stellar obliquities. We find that RLO tilts host stars into spin–orbit alignment (within a few ∼tens of degrees) regardless of initial conditions. Obliquity damping by RLO can only be reversed by the presence of misaligned companion planets within ≲2 au. While tides and mass transfer usually produce stellar spin-up, host stars can also emerge from RLO slowly rotating if systems begin strongly retrograde; retrograde RLO reconciles theory with the anomalously slow rotation of the desert-dweller host, LTT 9779. Predicted spin–orbit alignment may differentiate RLO from alternative giant planet destruction mechanisms, in particular hot Jupiter disruption during high-eccentricity migration (which tends to produce broadly distributed stellar obliquities). We summarize other population-level predictions that can further distinguish RLO from high-eccentricity migration. Our work suggests that follow-up obliquity measurements may reveal the formation pathways of desert dwellers and potentially open a window into gas giants’ exposed interiors.
Date Issued
2026-07-01
Date Acceptance
2026-05-15
Citation
The Astrophysical Journal Letters, 2026, 1005 (1)
ISSN
2041-8205
Publisher
American Astronomical Society
Journal / Book Title
The Astrophysical Journal Letters
Volume
1005
Issue
1
Copyright Statement
© 2026. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
License URL
Publication Status
Published
Article Number
L17
Date Publish Online
2026-06-25