Article Dans Une Revue Nature Année : 2024

A warm Neptuneu2019s methane reveals core mass and vigorous atmospheric mixing

David K. Sing
  • Fonction : Auteur
Zafar Rustamkulov
Daniel P. Thorngren
  • Fonction : Auteur
Elena Manjavacas
  • Fonction : Auteur
Joanna K. Barstow
Catarina Alves de Oliveira
  • Fonction : Auteur
Stephan M. Birkmann
Pierre Ferruit
Tracy L. Beck
  • Fonction : Auteur
Néstor Espinoza
Amélie Gressier
  • Fonction : Auteur
Jeff A. Valenti
Ryan C. Challener
  • Fonction : Auteur
Nikole K. Lewis
  • Fonction : Auteur
Nicolas Crouzet
Giovanna Giardino
  • Fonction : Auteur
Elspeth K.H. Lee
  • Fonction : Auteur
Roberto Maiolino
Bernard J. Rauscher
Marco Sirianni

Résumé

© The Author(s) 2024.Observations of transiting gas giant exoplanets have revealed a pervasive depletion of methane1u20134, which has only recently been identified atmospherically5,6. The depletion is thought to be maintained by disequilibrium processes such as photochemistry or mixing from a hotter interior7u20139. However, the interiors are largely unconstrained along with the vertical mixing strength and only upper limits on the CH4 depletion have been available. The warm Neptune WASP-107b stands out among exoplanets with an unusually low density, reported low core mass10, and temperatures amenable to CH4, though previous observations have yet to find the molecule2,4. Here we present a JWST-NIRSpec transmission spectrum of WASP-107b that shows features from both SO2 and CH4 along with H2O, CO2, and CO. We detect methane with 4.2σ significance at an abundance of 1.0 ± 0.5 ppm, which is depleted by 3 orders of magnitude relative to equilibrium expectations. Our results are highly constraining for the atmosphere and interior, which indicate the envelope has a super-solar metallicity of 43 ± 8 × solar, a hot interior with an intrinsic temperature of Tint = 460 ± 40 K, and vigorous vertical mixing which depletes CH4 with a diffusion coefficient of Kzz = 1011.6±0.1 cm2 s−1. Photochemistry has a negligible effect on the CH4 abundance but is needed to account for the SO2. We infer a core mass of 11.5−3.6+3.0M⊕, which is much higher than previous upper limits10, releasing a tension with core-accretion models11.
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hal-04626860 , version 1 (02-09-2024)

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David K. Sing, Zafar Rustamkulov, Daniel P. Thorngren, Elena Manjavacas, Joanna K. Barstow, et al.. A warm Neptuneu2019s methane reveals core mass and vigorous atmospheric mixing. Nature, 2024, ⟨10.1038/s41586-024-07395-z⟩. ⟨hal-04626860⟩
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