Atmospheres & Climate

Sulfur Dioxide and Other Molecular Species in the Atmosphere of the Sub-Neptune GJ 3470 b

By Keith Cowing
Status Report
June 11, 2024
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Sulfur Dioxide and Other Molecular Species in the Atmosphere of the Sub-Neptune GJ 3470 b
Three independent reductions of the NIRCam F322W2 and F444W data agree within their uncertainties The top panel shows the F322W2 and F444W transmission spectra, as reduced using the Pegasus, Eureka, and tshirt pipelines, plotted with their associated 1 σ uncertainties using constant 0.015µm-wide spectral bins. All of the F322W2 spectra have been offset down by 163 ppm to correct for a bias offset in the F322W2 transit depths compared to the F444W and Spitzer data (see Appendix B.3). All three reductions agree on the shape of the transmission spectrum and show features due to H2O (2.5–3.2µm), CH4 (3.2–3.5µm), SO2 (3.9–4.1µm), and CO2 (2.6–2.9µm and 4.2–4.5µm). The absorption cross sections of the prominent species in this wavelength range, many of which are visually identifiable in the bottom panel. — astro-ph.EP

We report observations of the atmospheric transmission spectrum of the sub-Neptune exoplanet GJ 3470 b taken using the Near-Infrared Camera (NIRCam) on JWST. Combined with two archival HST/WFC3 transit observations and fifteen archival Spitzer transit observations, we detect water, methane, sulfur dioxide, and carbon dioxide in the atmosphere of GJ 3470 b, each with a significance of >3-sigma.

GJ 3470 b is the lowest mass — and coldest — exoplanet known to show a substantial sulfur dioxide feature in its spectrum, at Mp=11.2M and Teq=600K. This indicates disequilibrium photochemistry drives sulfur dioxide production in exoplanet atmospheres over a wider range of masses and temperatures than has been reported or expected.

The water, carbon dioxide, and sulfur dioxide abundances we measure indicate an atmospheric metallicity of approximately 100× Solar. We see further evidence for disequilibrium chemistry in our inferred methane abundance, which is significantly lower than expected from equilibrium models consistent with our measured water and carbon dioxide abundances.

Thomas G. Beatty, Luis Welbanks, Everett Schlawin, Taylor J. Bell, Michael R. Line, Matthew Murphy, Isaac Edelman, Thomas P. Greene, Jonathan J. Fortney, Gregory W. Henry, Sagnick Mukherjee, Kazumasa Ohno, Vivien Parmentier, Emily Rauscher, Lindsey S. Wiser, Kenneth E. Arnold

Comments: 25 pages, 9 figures, 6 tables. Accepted in Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.04450 [astro-ph.EP] (or arXiv:2406.04450v1 [astro-ph.EP] for this version)
Submission history
From: Thomas Beatty
[v1] Thu, 6 Jun 2024 19:19:10 UTC (1,552 KB)

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) 🖖🏻