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Abstract WASP-107 b seems to be a poster child of the long-suspected high-eccentricity migration scenario. It is on a 5.7 day, polar orbit. The planet is Jupiter-like in radius but Neptune-like in mass with exceptionally low density. WASP-107 c is on a 1100 day,e= 0.28 orbit with at least Saturn mass. Planet b may still have a residual eccentricity of 0.06 ± 0.04: the ongoing tidal dissipation leads to the observed internally heated atmosphere and hydrodynamic atmospheric erosion. We present a population synthesis study coupling octupole Lidov–Kozai oscillations with various short-range forces, while simultaneously accounting for the radius inflation and tidal disruption of the planet. We find that a high-eccentricity migration scenario can successfully explain nearly all observed system properties. Our simulations further suggest that the initial location of WASP-107 b at the onset of migration is likely within the snowline (<0.5 au). More distant initial orbits usually lead to tidal disruption or orbit crossing. WASP-107 b most likely lost no more than 20% of its mass during the high-eccentricity migration, i.e., it did not form as a Jupiter-mass object. More vigorous tidally induced mass loss leads to disruption of the planet during migration. We predict that the current-day mutual inclination between the planets b and c is substantial: at least 25°–55°, which may be tested with future Gaia astrometric observations. Knowing the current-day mutual inclination may further constrain the initial orbit of planet b. We suggest that the proposed high-eccentricity migration scenario of WASP-107 may be applicable to HAT-P-11, GJ-3470, HAT-P-18, and GJ-436, which have similar orbital architectures.
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This content will become publicly available on May 15, 2026
From Tides to Currents: Unraveling the Mechanism that Powers WASP-107b’s Internal Heat Flux
Abstract The sub-Jovian exoplanet WASP-107b ranks among the best-characterized low-density worlds, featuring a Jupiter-like radius and a mass that lies firmly in the sub-Saturn range. Recently obtained JWST spectra reveal significant methane depletion in the atmosphere, indicating that WASP-107b’s envelope has both a high metallicity and an elevated internal heat flux. Together with a detected nonzero orbital eccentricity, these data have been interpreted as evidence of tidal heating. However, explaining the observed luminosity with tidal dissipation requires an unusually low tidal quality factor ofQ∼ 100. Moreover, we find that secular excitation by the radial-velocity-detected outer companion WASP-107c generally cannot sustain WASP-107b’s eccentricity in steady state against tidal circularization. As an alternative explanation, we propose that ohmic dissipation—generated by interactions between zonal flows and the planetary magnetic field in a partially ionized atmosphere—maintains the observed thermal state. Under nominal assumptions for the field strength, atmospheric circulation, and ionization chemistry, we show that ohmic heating readily accounts for WASP-107b’s inflated radius and anomalously large internal entropy.
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- Award ID(s):
- 2408867
- PAR ID:
- 10634579
- Publisher / Repository:
- AAS Journals
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 985
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 87
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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