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 and Peter McGill
Additional contact information
Eliza M.-R. Kempton: University of Maryland
Michael Zhang: University of Chicago
Jacob L. Bean: University of Chicago
Maria E. Steinrueck: Max-Planck Institute for Astronomy
Anjali A. A. Piette: Carnegie Institution for Science
Vivien Parmentier: University of Oxford
Isaac Malsky: University of Michigan
Michael T. Roman: University of Leicester
Emily Rauscher: University of Michigan
Peter Gao: Carnegie Institution for Science
Taylor J. Bell: NASA Ames Research Center
Qiao Xue: University of Chicago
Jake Taylor: University of Oxford
Arjun B. Savel: University of Maryland
Kenneth E. Arnold: University of Maryland
Matthew C. Nixon: University of Maryland
Kevin B. Stevenson: Johns Hopkins Applied Physics Laboratory
Megan Mansfield: University of Arizona
Sarah Kendrew: Space Telescope Science Institute
Sebastian Zieba: Max-Planck Institute for Astronomy
Elsa Ducrot: Marie Sklodowska-Curie Action
Achrène Dyrek: University of Paris-Saclay, University of Paris
Pierre-Olivier Lagage: University of Paris-Saclay, University of Paris
Keivan G. Stassun: Vanderbilt University
Gregory W. Henry: Tennessee State University
Travis Barman: University of Arizona
Roxana Lupu: Eureka Scientific, Inc.
Matej Malik: University of Maryland
Tiffany Kataria: California Institute of Technology
Jegug Ih: University of Maryland
Guangwei Fu: Johns Hopkins University
Luis Welbanks: Arizona State University
Peter McGill: University of California

Nature, 2023, vol. 620, issue 7972, 67-71

Abstract: 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 radii2,3. 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 hypothesis5–14. 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.

Date: 2023
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DOI: 10.1038/s41586-023-06159-5

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