Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b
Authors: Bell Taylor J. , Crouzet Nicolas , Cubillos Patricio E. , Kreidberg Laura , Piette Anjali A. A. , Roman Michael T. , Barstow Joanna K. , Blecic Jasmina , Carone Ludmila , Coulombe Louis-Philippe , Ducrot Elsa , Hammond Mark , Mendonça João M. , Moses Julianne I. , Parmentier Vivien , Stevenson Kevin B. , Teinturier Lucas , Zhang Michael , Batalha Natalie M. , Bean Jacob L. , Benneke Björn , Charnay Benjamin , Chubb Katy L. , Demory Brice-Olivier , Gao Peter , Lee Elspeth K. H. , López-Morales Mercedes , Morello Giuseppe , Rauscher Emily , Sing David K. , Tan Xianyu , Venot Olivia , Wakeford Hannah R. , Aggarwal Keshav , Ahrer Eva-Maria , Alam Munazza K. , Baeyens Robin , Barrado David , Caceres Claudio , Carter Aarynn L. , Casewell Sarah L. , Challener Ryan C. , Crossfield Ian J. M. , Decin Leen , Désert Jean-Michel , Dobbs-Dixon Ian , Dyrek Achrène , Espinoza Néstor , Feinstein Adina D. , Gibson Neale P. , Harrington Joseph , Helling Christiane , Hu Renyu , Iro Nicolas , Kempton Eliza M.-R. , Kendrew Sarah , Komacek Thaddeus D. , Krick Jessica , Lagage Pierre-Olivier , Leconte Jérémy , Lendl Monika , Lewis Neil T. , Lothringer Joshua D. , Malsky Isaac , Mancini Luigi , Mansfield Megan , Mayne Nathan J. , Evans-Soma Thomas M. , Molaverdikhani Karan , Nikolov Nikolay K. , Nixon Matthew C. , Palle Enric , Petit dit de la Roche Dominique J. M. , Piaulet Caroline , Powell Diana , Rackham Benjamin V. , Schneider Aaron D. , Steinrueck Maria E. , Taylor Jake , Welbanks Luis , Yurchenko Sergei N. , Zhang Xi , Zieba Sebastian 
Published: April 2024

Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5 μm to 12 μm with the JWST’s Mid-Infrared Instrument. The spectra reveal a large day–night temperature contrast (with average brightness temperatures of 1,524 ± 35 K and 863 ± 23 K, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase-curve shape and emission spectra strongly suggest the presence of nightside clouds that become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1–6 ppm, depending on model assumptions). Our results provide strong evidence that the atmosphere of WASP-43b is shaped by disequilibrium processes and provide new insights into the properties of the planet’s nightside clouds. However, the remaining discrepancies between our observations and our predictive atmospheric models emphasize the importance of further exploring the effects of clouds and disequilibrium chemistry in numerical models.