Dynamical Tides during High-eccentricity Migration Produce the Hot-Jupiter Pileup, Neptune Ridge, and Neptune Desert
- 1The Pennsylvania State University
- 2Institute for Theory & Computation
Abstract
The period distribution of hot gaseous exoplanets depends strongly on mass. Clustering between the orbital periods of ∼3 to ∼5–6 days is seen for sub-Saturns (“Neptune ridge”) and Jovians (“hot-Jupiter pileup”), contrasting with a sharp deficit interior to 3 days for sub-Saturns, not seen for Jovians (“Neptune desert”). During high-eccentricity migration, tidally excited fundamental-modes ( f -modes) act as a reservoir for orbital energy, and can take gaseous planets formed beyond several astronomical units and place them at short separations. However, how f -modes relinquish their energy into the planet interior is unknown. Here, we show how f -modes can not only circularize orbits—causing clustering near the Neptune ridge and hot-Jupiter pileup—but can also shock and unbind mass, leaving sub-Saturn cores in the Neptune desert. Our hydrodynamical simulations demonstrate that close approaches tidally excite f -modes, whose supersonic velocities shock gaseous envelopes. Atmospheres cool by radiative diffusion or winds when shocks penetrate shallow versus deep depths. Planetary structural and orbital evolution is followed over many periastron passages using an iterative map: shocks that diffusively cool circularize and bunch orbits near the hot-Jupiter pileup and Neptune ridge, while shocks that drive outflows unbind envelopes and place gas-giant cores in the Neptune desert. Sub-Saturns that dwell in the desert are predicted to arrive with large spin–orbit misalignments after producing luminous flares.
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BibTeX
@article{zanazzi2026dynamical,
title = {{Dynamical Tides during High-eccentricity Migration Produce the Hot-Jupiter Pileup, Neptune Ridge, and Neptune Desert}},
author = {J. J. Zanazzi and Morgan MacLeod and Marta L. Bryan and Suvrath Mahadevan},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/ae9e27},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9e27},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Dynamical Tides during High-eccentricity Migration Produce the Hot-Jupiter Pileup, Neptune Ridge, and Neptune Desert
AU - J. J. Zanazzi
AU - Morgan MacLeod
AU - Marta L. Bryan
AU - Suvrath Mahadevan
PY - 2026
DA - 2026/10/15
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae9e27
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ae9e27
AB - The period distribution of hot gaseous exoplanets depends strongly on mass. Clustering between the orbital periods of ∼3 to ∼5–6 days is seen for sub-Saturns (“Neptune ridge”) and Jovians (“hot-Jupiter pileup”), contrasting with a sharp deficit interior to 3 days for sub-Saturns, not seen for Jovians (“Neptune desert”). During high-eccentricity migration, tidally excited fundamental-modes ( f -modes) act as a reservoir for orbital energy, and can take gaseous planets formed beyond several astronomical units and place them at short separations. However, how f -modes relinquish their energy into the planet interior is unknown. Here, we show how f -modes can not only circularize orbits—causing clustering near the Neptune ridge and hot-Jupiter pileup—but can also shock and unbind mass, leaving sub-Saturn cores in the Neptune desert. Our hydrodynamical simulations demonstrate that close approaches tidally excite f -modes, whose supersonic velocities shock gaseous envelopes. Atmospheres cool by radiative diffusion or winds when shocks penetrate shallow versus deep depths. Planetary structural and orbital evolution is followed over many periastron passages using an iterative map: shocks that diffusively cool circularize and bunch orbits near the hot-Jupiter pileup and Neptune ridge, while shocks that drive outflows unbind envelopes and place gas-giant cores in the Neptune desert. Sub-Saturns that dwell in the desert are predicted to arrive with large spin–orbit misalignments after producing luminous flares.
SN - 0004-637X
SN - 1538-4357
ER -