Photochemically-produced SO$_2$ in the atmosphere of WASP-39b
Creators: name: Tsai, Shang-Min
name: Lee, Elspeth K. H.
name: Powell, Diana
name: Gao, Peter
name: Zhang, Xi
name: Moses, Julianne
name: Hébrard, Eric
name: Venot, Olivia
name: Parmentier, Vivien
name: Jordan, Sean
name: Hu, Renyu
name: Alam, Munazza K.
name: Alderson, Lili
name: Batalha, Natalie M.
name: Bean, Jacob L.
name: Benneke, Björn
name: Bierson, Carver J.
name: Brady, Ryan P.
name: Carone, Ludmila
name: Carter, Aarynn L.
name: Chubb, Katy L.
name: Inglis, Julie
name: Leconte, Jérémy
name: Lopez-Morales, Mercedes
name: Miguel, Yamila
name: Molaverdikhani, Karan
name: Rustamkulov, Zafar
name: Sing, David K.
name: Stevenson, Kevin B.
name: Wakeford, Hannah R
name: Yang, Jeehyun
name: Aggarwal, Keshav
name: Baeyens, Robin
name: Barat, Saugata
name: Borro, Miguel de Val
name: Daylan, Tansu
name: Fortney, Jonathan J.
name: France, Kevin
name: Goyal, Jayesh M
name: Grant, David
name: Kirk, James
name: Kreidberg, Laura
name: Louca, Amy
name: Moran, Sarah E.
name: Mukherjee, Sagnick
name: Nasedkin, Evert
name: Ohno, Kazumasa
name: Rackham, Benjamin V.
name: Redfield, Seth
name: Taylor, Jake
name: Tremblin, Pascal
name: Visscher, Channon
name: Wallack, Nicole L.
name: Welbanks, Luis
name: Youngblood, Allison
name: Ahrer, Eva-Maria
name: Batalha, Natasha E.
name: Behr, Patrick
name: Berta-Thompson, Zachory K.
name: Blecic, Jasmina
name: Casewell, S. L.
name: Crossfield, Ian J. M.
name: Crouzet, Nicolas
name: Cubillos, Patricio E.
name: Decin, Leen
name: Désert, Jean-Michel
name: Feinstein, Adina D.
name: Gibson, Neale P.
name: Harrington, Joseph
name: Heng, Kevin
name: Henning, Thomas
name: Kempton, Eliza M. -R.
name: Krick, Jessica
name: Lagage, Pierre-Olivier
name: Lendl, Monika
name: Line, Michael
name: Lothringer, Joshua D.
name: Mansfield, Megan
name: Mayne, N. J.
name: Mikal-Evans, Thomas
name: Palle, Enric
name: Schlawin, Everett
name: Shorttle, Oliver
name: Wheatley, Peter J.
name: Yurchenko, Sergei N.
Publisher: name: arXiv
Year: 2022
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability. However, no unambiguous photochemical products have been detected in exoplanet atmospheres to date. Recent observations from the JWST Transiting Exoplanet Early Release Science Program found a spectral absorption feature at 4.05 $μ$m arising from SO$_2$ in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 M$_J$) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of $\sim$1100 K. The most plausible way of generating SO$_2$ in such an atmosphere is through photochemical processes. Here we show that the SO$_2$ distribution computed by a suite of photochemical models robustly explains the 4.05 $μ$m spectral feature identified by JWST transmission observations with NIRSpec PRISM (2.7$σ$) and G395H (4.5$σ$). SO$_2$ is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H$_2$S) is destroyed. The sensitivity of the SO$_2$ feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of $\sim$10$\times$ solar. We further point out that SO$_2$ also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.
description: 39 pages, 14 figures, accepted to be published in Nature