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An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet.

Hellier; Smalley

An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet. Thumbnail


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Abstract

Broad absorption signatures from alkali metals, such as the sodium (Na I) and potassium (K I) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6. Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9. Here we report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. We are able to measure a precise, absolute sodium abundance of logeNa?=?[Formula: see text], and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Zp/Z??=?[Formula: see text]). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets10-12.

Acceptance Date Jan 30, 2018
Publication Date May 7, 2018
Publicly Available Date Mar 28, 2024
Journal Nature
Print ISSN 1476-4687
Publisher Nature Publishing Group
Pages 526 - 529
DOI https://doi.org/10.1038/s41586-018-0101-7
Publisher URL https://doi.org/10.1038/s41586-018-0101-7

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