Possible Carbon Dioxide above the Thick Aerosols of GJ 1214 b

Possible Carbon Dioxide above the Thick Aerosols of GJ 1214 b

Sub-Neptune planets with radii smaller than Neptune (3.9 R _⊕ ) are the most common type of planet known to exist in the Milky Way, even though they are absent in the solar system. These planets can potentially have a large diversity of compositions as a result of different mixtures of rocky materia...

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Main Authors: Everett Schlawin, Kazumasa Ohno, Taylor J. Bell, Matthew M. Murphy, Luis Welbanks, Thomas G. Beatty, Thomas P. Greene, Jonathan J. Fortney, Vivien Parmentier, Isaac R. Edelman, Samuel Gill, David R. Anderson, Peter J. Wheatley, Gregory W. Henry, Nishil Mehta, Laura Kreidberg, Marcia J. Rieke
Format: Article
Language:English
Published: IOP Publishing 2024-01-01
Series:The Astrophysical Journal Letters
Subjects:
Exoplanet atmospheric composition
Exoplanet atmospheres
Mini Neptunes
James Webb Space Telescope
Transmission spectroscopy
Online Access:https://doi.org/10.3847/2041-8213/ad7fef
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Summary:Sub-Neptune planets with radii smaller than Neptune (3.9 R _⊕ ) are the most common type of planet known to exist in the Milky Way, even though they are absent in the solar system. These planets can potentially have a large diversity of compositions as a result of different mixtures of rocky material, icy material, and gas accreted from a protoplanetary disk. However, the bulk density of a sub-Neptune, informed by its mass and radius alone, cannot uniquely constrain its composition; atmospheric spectroscopy is necessary. GJ 1214 b, which hosts an atmosphere that is potentially the most favorable for spectroscopic detection of any sub-Neptune, is instead enshrouded in aerosols (thus showing no spectroscopic features), hiding its composition from view at previously observed wavelengths in its terminator. Here, we present a JWST NIRSpec transmission spectrum from 2.8 to 5.1 μ m that shows signatures of CO _2 and CH _4 , expected at high metallicity. A model containing both these molecules is preferred by 3.3 σ and 3.6 σ as compared to a featureless spectrum for two different data analysis pipelines, respectively. Given the low signal-to-noise of the features compared to the continuum, however, more observations are needed to confirm the CO _2 and CH _4 signatures and better constrain other diagnostic features in the near-infrared. Further modeling of the planet’s atmosphere, interior structure and origins will provide valuable insights about how sub-Neptunes like GJ 1214 b form and evolve.
ISSN:2041-8205

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