Exoplanetology: Exoplanets & Exomoons

Possible Carbon Dioxide Above The Thick Aerosols Of sub-Neptune GJ 1214 b

By Keith Cowing
Status Report
astro-ph.EP
October 21, 2024
Filed under , , , , , , ,
Possible Carbon Dioxide Above The Thick Aerosols Of sub-Neptune GJ 1214 b
2D light curves binned to a resolution of R=100 and 40 time bins for NRS2 (top row) and NRS1 (bottom row), with both transits averaged. The normalized flux in percentage (after linearly de-trending at each wavelength) is shown in panel A. The differential time series, after dividing by the broadband for a given detector is shown in ppm in panel B. The differential light curve model is shown in panel C and the residuals of the light curve subtracted by the model are shown in panel D. The start of ingress and end of egress times are marked as vertical dashed lines. Increased and decreased transit depths relative to the broadband light curve are visible as dark and bright bands between ingress and egress. The most noticeable features are increased transit depths near 4.3 µm and 2.8 µm and decreased transit depths near 3.6 µm and 4.6 µm. — astro-ph.EP

Sub-Neptune planets with radii smaller than Neptune (3.9 Re) 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 um that shows signatures of carbon dioxide and methane, expected at high metallicity.

A model containing both these molecules is preferred by 3.3 and 3.6 sigma 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 carbon dioxide and methane 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.

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

Comments: 22 pages, 11 figures, Accepted in ApJL, Please also see a companion paper Ohno et al. (2024)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2410.10183 [astro-ph.EP] (or arXiv:2410.10183v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2410.10183
Focus to learn more
Submission history
From: Everett Schlawin
[v1] Mon, 14 Oct 2024 06:09:06 UTC (1,739 KB)
https://arxiv.org/abs/2410.10183

Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

Follow on Twitter
MORE FROM Exoplanetology: Exoplanets & Exomoons