Imaging & Spectroscopy

Direct Evidence of Photochemistry In An Exoplanet Atmosphere

By Keith Cowing
Press Release
November 21, 2022
Filed under , , , , , , , ,
Direct Evidence of Photochemistry In An Exoplanet Atmosphere
Morning and evening terminator averaged theoretical transmission spectra generated from 1D photochemical model results. Top left: Comparison to the NIRSpec PRISM FIREFly reduction (Rustamkulov et al.(submitted)). Top right: Comparison to the NIRSpec G395H weighted-mean reduction (Alderson et al.(submitted)). Bottom left: Comparison to the current HST and VLT/FORS2 optical wavelength data [20, 21], the models show pronounced features at UV wavelengths due to sulphur species compared to the model without S bearing species (dashed blue line). Bottom right: Predicted spectra across the MIRI LRS wavelength range. — astro-ph.EP

Photochemistry is a fundamental process of planetary atmospheres that is integral to habitability, atmospheric composition and stability, and aerosol formation. However, no unambiguous photochemical products have been detected in exoplanet atmospheres to date.

Here we show that photochemically produced sulphur dioxide (SO2) is present in the atmosphere of the hot, giant exoplanet WASP-39b, as constrained by data from the JWST Transiting Exoplanet Early Release Science Program and informed by a suite of photochemical models.

We find that SO2 is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H2S) is destroyed. The SO2 distribution computed by the photochemical models robustly explains the 4.05 μm spectral feature seen in JWST transmission spectra [Rustamkulov et al.(submitted), Alderson et al.(submitted)] and leads to observable features at ultraviolet and thermal infrared wavelengths not available from the current observations.

The sensitivity of the SO2 feature to the enrichment of heavy elements in the atmosphere (“metallicity”) suggests that it can be used as a powerful tracer of atmospheric properties, with our results implying a metallicity of ∼10× solar for WASP-39b. Through providing improved constraints on bulk metallicity and sulphur abundance, the detection of SO2 opens a new avenue for the investigation of giant-planet formation.

Our work demonstrates that sulphur photochemistry may be readily observable for exoplanets with super-solar metallicity and equilibrium temperatures ≳750 K. The confirmation of photochemistry through the agreement between theoretical predictions and observational data is pivotal for further atmospheric characterisation studies.

Shang-Min Tsai, Elspeth K. H. Lee, Diana Powell, Peter Gao, Xi Zhang, Julianne Moses, Eric Hébrard, Olivia Venot, Vivien Parmentier, Sean Jordan, Renyu Hu, Munazza K. Alam, Lili Alderson, Natalie M. Batalha, Jacob L. Bean, Björn Benneke, Carver J. Bierson, Ryan P. Brady, Ludmila Carone, Aarynn L. Carter, Katy L. Chubb, Julie Inglis, Jérémy Leconte, Mercedes Lopez-Morales, Yamila Miguel, Karan Molaverdikhani, Zafar Rustamkulov, David K. Sing, Kevin B. Stevenson, Hannah R Wakeford, Jeehyun Yang, Keshav Aggarwal, Robin Baeyens, Saugata Barat, Miguel de Val Borro, Tansu Daylan, Jonathan J. Fortney, Kevin France, Jayesh M Goyal, David Grant, James Kirk, Laura Kreidberg, Amy Louca, Sarah E. Moran, Sagnick Mukherjee, Evert Nasedkin, Kazumasa Ohno, Benjamin V. Rackham, Seth Redfield, Jake Taylor, Pascal Tremblin, Channon Visscher, Nicole L. Wallack, Luis Welbanks, Allison Youngblood, Eva-Maria Ahrer, Natasha E. Batalha, Patrick Behr, Zachory K. Berta-Thompson, Jasmina Blecic, S.L. Casewell, Ian J.M. Crossfield, Nicolas Crouzet, Patricio E. Cubillos, Leen Decin, Jean-Michel Désert, Adina D. Feinstein, Neale P. Gibson, Joseph Harrington, Keivn Heng, Thomas Henning, Eliza M.-R. Kempton, Jessica Krick, Pierre-Olivier Lagage, Monika Lendl, Michael Line, Joshua D. Lothringer, Megan Mansfield, N. J. Mayne, Thomas Mikal-Evans, Enric Palle, Everett Schlawin, Oliver Shorttle, Peter J. Wheatley, Sergei N. Yurchenko

Comments: 40 pages, 13 figures, under review at Nature
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2211.10490 [astro-ph.EP] (or arXiv:2211.10490v1 [astro-ph.EP] for this version)
Submission history
From: Shang-Min Tsai
[v1] Fri, 18 Nov 2022 19:57:16 UTC (2,290 KB)

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