Identification of carbon dioxide in an exoplanet atmosphere
Authors:   JWST Transiting Exoplanet Community Early Release Science Team, Ahrer Eva-Maria , Alderson Lili , Batalha Natalie M. , Batalha Natasha E. , Bean Jacob L. , Beatty Thomas G. , Bell Taylor J. , Benneke Björn , Berta-Thompson Zachory K. , Carter Aarynn L. , Crossfield Ian J. M. , Espinoza Néstor , Feinstein Adina D. , Fortney Jonathan J. , Gibson Neale P. , Goyal Jayesh M. , Kempton Eliza M.-R. , Kirk James , Kreidberg Laura , López-Morales Mercedes , Line Michael R. , Lothringer Joshua D. , Moran Sarah E. , Mukherjee Sagnick , Ohno Kazumasa , Parmentier Vivien , Piaulet Caroline , Rustamkulov Zafar , Schlawin Everett , Sing David K. , Stevenson Kevin B. , Wakeford Hannah R. , Allen Natalie H. , Birkmann Stephan M. , Brande Jonathan , Crouzet Nicolas , Cubillos Patricio E. , Damiano Mario , Désert Jean-Michel , Gao Peter , Harrington Joseph , Hu Renyu , Kendrew Sarah , Knutson Heather A. , Lagage Pierre-Olivier , Leconte Jérémy , Lendl Monika , MacDonald Ryan J. , May E. M. , Miguel Yamila , Molaverdikhani Karan , Moses Julianne I. , Murray Catriona Anne , Nehring Molly , Nikolov Nikolay K. , Petit dit de la Roche D. J. M. , Radica Michael , Roy Pierre-Alexis , Stassun Keivan G. , Taylor Jake , Waalkes William C. , Wachiraphan Patcharapol , Welbanks Luis , Wheatley Peter J. , Aggarwal Keshav , Alam Munazza K. , Banerjee Agnibha , Barstow Joanna K. , Blecic Jasmina , Casewell S. L. , Changeat Quentin , Chubb K. L. , Colón Knicole D. , Coulombe Louis-Philippe , Daylan Tansu , de Val-Borro Miguel , Decin Leen , Dos Santos Leonardo A. , Flagg Laura , France Kevin , Fu Guangwei , García Muñoz A. , Gizis John E. , Glidden Ana , Grant David , Heng Kevin , Henning Thomas , Hong Yu-Cian , Inglis Julie , Iro Nicolas , Kataria Tiffany , Komacek Thaddeus D. , Krick Jessica E. , Lee Elspeth K. H. , Lewis Nikole K. , Lillo-Box Jorge , Lustig-Yaeger Jacob , Mancini Luigi , Mandell Avi M. , Mansfield Megan , Marley Mark S. , Mikal-Evans Thomas , Morello Giuseppe , Nixon Matthew C. , Ortiz Ceballos Kevin , Piette Anjali A. A. , Powell Diana , Rackham Benjamin V. , Ramos-Rosado Lakeisha , Rauscher Emily , Redfield Seth , Rogers Laura K. , Roman Michael T. , Roudier Gael M. , Scarsdale Nicholas , Shkolnik Evgenya L. , Southworth John , Spake Jessica J. , Steinrueck Maria E. , Tan Xianyu , Teske Johanna K. , Tremblin Pascal , Tsai Shang-Min , Tucker Gregory S. , Turner Jake D. , Valenti Jeff A. , Venot Olivia , Waldmann Ingo P. , Wallack Nicole L. , Zhang Xi , Zieba Sebastian 
Published: September 2022

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2is an indicator of the metal enrichment (that is, elements heavier than helium, also called ‘metallicity’)1–3, and thus the formation processes of the primary atmospheres of hot gas giants4–6. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets7–9. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification10–12. Here we present the detection of CO2in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme13,14. The data used in this study span 3.0–5.5 micrometres in wavelength and show a prominent CO2absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative–convective–thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models.