Nikolov, N, Sing, DK, Fortney, JJ, Goyal, JM, Drummond, B, Evans, TM, Gibson, NP, De Mooij, EJW, Rustamkulov, Z, Wakeford, HR, Smalley, B, Burgasser, AJ, Hellier, C, Helling, C, Mayne, NJ, Madhusudhan, N, Kataria, T, Baines, J, Carter, AL, Ballester, GE, Barstow, JK, McCleery, J and Spake, JJ (2018) An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet. Nature, 557 (7706). 526 - 529. ISSN 1476-4687

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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 logεNa = [Formula: see text], and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Zp/Zʘ = [Formula: see text]). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets10-12.

Item Type: Article
Additional Information: This is the accepted author manuscript (AAM). The final published version (version of record) is available online via Nature Publishing Group at Please refer to any applicable terms of use of the publisher.
Subjects: Q Science > QB Astronomy
Q Science > QB Astronomy > QB460 Astrophysics
Q Science > QB Astronomy > QB600 Planets. Planetology
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Related URLs:
Depositing User: Symplectic
Date Deposited: 16 Jul 2018 10:26
Last Modified: 07 Nov 2018 01:30

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