A warm Neptune's methane reveals core mass and vigorous atmospheric mixing

• 成果类型: Article
• 署名作者: Sing, David K.; Rustamkulov, Zafar; Thorngren, Daniel P.; Barstow, Joanna K.; Tremblin, Pascal; de Oliveira, Catarina Alves; Beck, Tracy L.; Birkmann, Stephan M.; Challener, Ryan C.; Crouzet, Nicolas; Espinoza, Nestor; Ferruit, Pierre; Giardino, Giovanna; Gressier, Amelie; Lee, Elspeth K. H.; Lewis, Nikole K.; Maiolino, Roberto; Manjavacas, Elena; Rauscher, Bernard J.; Sirianni, Marco; Valenti, Jeff A.
• 署名单位: Johns Hopkins University; Johns Hopkins University; Open University - UK; Universite Paris Saclay; CEA; Centre National de la Recherche Scientifique (CNRS); Universite Paris Saclay; CEA; Centre National de la Recherche Scientifique (CNRS); Universite Paris Cite; European Space Agency; European Space Astronomy Center; Space Telescope Science Institute; Cornell University; Leiden University; Leiden University - Excl LUMC; European Space Agency; European Space Research & Technology Centre; University of Bern; University of Cambridge; Space Telescope Science Institute; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; Space Telescope Science Institute
• 刊物名称: Nature
• ISSN/ISSBN: 0028-4165
• DOI: 10.1038/s41586-024-07395-z
• 发表日期: 2024-06-27
• 关键词: molecular line lists; collision-induced absorption; rotation-vibration spectrum; h-2 pairs; exoplanet; efficient; planets; coefficients; SCATTERING; EVOLUTION

摘要

Observations of transiting gas giant exoplanets have revealed a pervasive depletion of methane 1-4 , which has only recently been identified atmospherically 5,6 . The depletion is thought to be maintained by disequilibrium processes such as photochemistry or mixing from a hotter interior 7-9 . 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 mass 10 , and temperatures amenable to CH4, though previous observations have yet to find the molecule 2,4 . 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 4.2 sigma 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 x solar, a hot interior with an intrinsic temperature of T int = 460 +/- 40 K, and vigorous vertical mixing which depletes CH4 with a diffusion coefficient of K zz = 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 + 3.0 M circle plus \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${11.5}_{-3.6}<^>{+3.0}{M}_{\oplus }$$\end{document} , which is much higher than previous upper limits 10 , releasing a tension with core-accretion models 11 . Observations of the warm Neptune WASP-107b show that the planet has a hot interior with an intrinsic temperature of about 460 K.