A reflective, metal

Nov 22, 2023

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There are no planets intermediate in size between Earth and Neptune in our Solar System, yet these objects are found around a substantial fraction of other stars [1]. Population statistics show that close-in planets in this size range bifurcate into two classes based on their radii [2, 3]. It is hypothesized that the group with larger radii (referred to as "sub-Neptunes") is distinguished by having hydrogen-dominated atmospheres that are a few percent of the total mass of the planets [4]. GJ 1214b is an archetype sub-Neptune that has been observed extensively using transmission spectroscopy to test this hypothesis [5-14]. However, themeasured spectra are featureless, and thus inconclusive, due to the presence of high-altitude aerosols in the planet's atmosphere. Here we report a spectroscopic thermal phase curve of GJ 1214b obtained with JWST in the mid-infrared. The dayside and nightside spectra (average brightness temperatures of 553 ± 9 and 437 ± 19 K, respectively) each show >3σ evidence of absorption features, with H2O as the most likely cause in both. The measured global thermal emission implies that GJ 1214b's Bond albedo is 0.51 ± 0.06. Comparison between the spectroscopic phase curve data and three-dimensional models of GJ 1214b reveal a planet with a high metallicity atmosphere blanketed by a thick and highly reflective layer of clouds or haze.

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Department of Astronomy, University of Maryland, College Park, MD, USA

Eliza M.-R. Kempton, Arjun B. Savel, Kenneth E. Arnold, Matthew C. Nixon, Matej Malik & Jegug Ih

Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL, USA

Michael Zhang, Jacob L. Bean & Qiao Xue

Max-Planck-Institut für Astronomie, Heidelberg, Germany

Maria E. Steinrueck & Sebastian Zieba

Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA

Anjali A. A. Piette & Peter Gao

Department of Physics, University of Oxford, Oxford, UK

Vivien Parmentier & Jake Taylor

Department of Astronomy, University of Michigan, Ann Arbor, MI, USA

Isaac Malsky & Emily Rauscher

School of Physics and Astronomy, University of Leicester, Leicester, UK

Michael T. Roman

BAER Institute, NASA Ames Research Center, Moffet Field, CA, USA

Taylor J. Bell

Institut Trottier de Recherche sur les Exoplanètes and Département de Physique, Université de Montréal, Montréal, QC, Canada

Jake Taylor

Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA

Arjun B. Savel

Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA

Kevin B. Stevenson

Steward Observatory, University of Arizona, Tucson, AZ, USA

Megan Mansfield

European Space Agency, Space Telescope Science Institute, Baltimore, MD, USA

Sarah Kendrew

Leiden Observatory, Leiden University, Leiden, The Netherlands

Sebastian Zieba

Paris Region Fellow, Marie Sklodowska-Curie Action, Paris, France

Elsa Ducrot

AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, Gif-sur-Yvette, France

Elsa Ducrot, Achrène Dyrek & Pierre-Olivier Lagage

Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA

Keivan G. Stassun

Center of Excellence in Information Systems, Tennessee State University, Nashville, TN, USA

Gregory W. Henry

Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

Travis Barman

Eureka Scientific, Inc., Oakland, CA, USA

Roxana Lupu

NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Tiffany Kataria

Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, USA

Guangwei Fu

School of Earth & Space Exploration, Arizona State University, Tempe, AZ, USA

Luis Welbanks

Department of Astronomy & Astrophysics, University of California, Santa Cruz, CA, USA

Peter McGill

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Correspondence to Eliza M.-R. Kempton.

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Kempton, E.MR., Zhang, M., Bean, J.L. et al. A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve. Nature (2023). https://doi.org/10.1038/s41586-023-06159-5

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Received: 11 February 2023

Accepted: 02 May 2023

Published: 10 May 2023

DOI: https://doi.org/10.1038/s41586-023-06159-5

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