A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve

Eliza M-R Kempton; Michael Zhang; Jacob L Bean; Maria E Steinrueck; Anjali A A Piette; Vivien Parmentier; Isaac Malsky; Michael T Roman; Emily Rauscher; Peter Gao; Taylor J Bell; Qiao Xue; Jake Taylor; Arjun B Savel; Kenneth E Arnold; Matthew C Nixon; Kevin B Stevenson; Megan Mansfield; Sarah Kendrew; Sebastian Zieba; Elsa Ducrot; Achrène Dyrek; Pierre-Olivier Lagage; Keivan G Stassun; Gregory W Henry; Travis Barman; Roxana Lupu; Matej Malik; Tiffany Kataria; Jegug Ih; Guangwei Fu; Luis Welbanks; Peter McGill

doi:10.1038/s41586-023-06159-5

A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve

Nature. 2023 Aug;620(7972):67-71. doi: 10.1038/s41586-023-06159-5. Epub 2023 May 10.

Authors

Eliza M-R Kempton¹, Michael Zhang², Jacob L Bean², Maria E Steinrueck³, Anjali A A Piette⁴, Vivien Parmentier^{5

6}, Isaac Malsky⁷, Michael T Roman⁸, Emily Rauscher⁷, Peter Gao⁴, Taylor J Bell⁹, Qiao Xue², Jake Taylor^{5

10}, Arjun B Savel^{11

12}, Kenneth E Arnold¹¹, Matthew C Nixon¹¹, Kevin B Stevenson¹³, Megan Mansfield¹⁴, Sarah Kendrew¹⁵, Sebastian Zieba^{3

16}, Elsa Ducrot^{17

18}, Achrène Dyrek¹⁸, Pierre-Olivier Lagage¹⁸, Keivan G Stassun¹⁹, Gregory W Henry²⁰, Travis Barman²¹, Roxana Lupu²², Matej Malik¹¹, Tiffany Kataria²³, Jegug Ih¹¹, Guangwei Fu²⁴, Luis Welbanks²⁵, Peter McGill²⁶

Affiliations

¹ Department of Astronomy, University of Maryland, College Park, MD, USA. ekempton@astro.umd.edu.
² Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
³ Max-Planck Institute for Astronomy, Heidelberg, Germany.
⁴ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA.
⁵ Department of Physics, University of Oxford, Oxford, UK.
⁶ Lagrange Laboratory, University of the Côte d'Azur, Observatory of the Côte d'Azur, CNRS, Nice, France.
⁷ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
⁸ School of Physics and Astronomy, University of Leicester, Leicester, UK.
⁹ BAER Institute, NASA Ames Research Center, Moffet Field, CA, USA.
¹⁰ Institut Trottier de Recherche sur les Exoplanètes and Department of Physics, University of Montréal, Montréal, Quebec, Canada.
¹¹ Department of Astronomy, University of Maryland, College Park, MD, USA.
¹² Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA.
¹³ Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA.
¹⁴ Steward Observatory, University of Arizona, Tucson, AZ, USA.
¹⁵ European Space Agency, Space Telescope Science Institute, Baltimore, MD, USA.
¹⁶ Leiden Observatory, Leiden University, Leiden, the Netherlands.
¹⁷ Paris Region Fellow, Marie Sklodowska-Curie Action, Paris, France.
¹⁸ AIM, CEA, CNRS, University of Paris-Saclay, University of Paris, Gif-sur-Yvette, France.
¹⁹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA.
²⁰ Center of Excellence in Information Systems, Tennessee State University, Nashville, TN, USA.
²¹ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
²² Eureka Scientific, Inc., Oakland, CA, USA.
²³ NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
²⁴ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA.
²⁵ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
²⁶ Department of Astronomy & Astrophysics, University of California, Santa Cruz, CA, USA.

PMID: 37164036
DOI: 10.1038/s41586-023-06159-5

Abstract

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 stars¹. Population statistics show that close-in planets in this size range bifurcate into two classes on the basis of their radii^2,3. It is proposed 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 planets⁴. GJ 1214b is an archetype sub-Neptune that has been observed extensively using transmission spectroscopy to test this hypothesis^5-14. However, the measured 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 the James Webb Space Telescope (JWST) in the mid-infrared. The dayside and nightside spectra (average brightness temperatures of 553 ± 9 and 437 ± 19 K, respectively) each show more than 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.