Webb Space Telescope Detects Carbon Dioxide in the Atmosphere of an Exoplanet

Filtered Starlight

Transiting planets like WASP-39 b, whose orbits we observe edge-on rather than from above, can provide scientists with ideal opportunities to investigate planetary atmospheres. During a transit, some of the starlight is eclipsed by the planet completely (causing the overall dimming) and some is transmitted through the planet’s atmosphere.

Because different gases absorb different combinations of colors, investigators can analyze small differences in brightness of the transmitted light across a spectrum of wavelengths to determine exactly what an atmosphere is made of. With its combination of an inflated atmosphere and frequent transits, WASP-39 b is an ideal target for transmission spectroscopy.

A series of light curves from Webb’s Near-Infrared Spectrograph (NIRSpec) shows the change in brightness of three different wavelengths (colors) of light from the WASP-39 star system over time as the planet transited the star on July 10, 2022. A transit occurs when an orbiting planet moves between the star and the telescope, blocking some of the light from the star.
This observation was made using the NIRSpec PRISM bright object time-series mode, which involves using a prism to spread out light from a single bright object (like the star WASP-39) and measure the brightness of each wavelength at set intervals of time.
To capture these data, Webb stared at the WASP-39 star system for more than eight hours, beginning about three hours before the transit and ending about two hours after the transit was complete. The transit itself lasted about three hours. Each curve shown here includes a total of 500 individual brightness measurements – about one per minute.
Although all colors are blocked to some extent by the planet, some colors are blocked more than others. This occurs because each gas in the atmosphere absorbs different amounts of specific wavelengths. As a result, each color has a slightly different light curve. During the transit of WASP-39 b, light with a wavelength of 4.3 microns is not as bright as 3.0-micron or 4.7-micron light because it is absorbed by carbon dioxide.
Credit: NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI)

First Clear Detection of Carbon Dioxide

The team of researchers used Webb’s Near-Infrared Spectrograph (NIRSpec) for its observations of WASP-39 b. In the resulting spectrum of the exoplanet’s atmosphere, a small hill between 4.1 and 4.6 microns presents the first clear, detailed evidence of carbon dioxide ever detected in a planet outside the solar system.

“As soon as the data appeared on my screen, the whopping carbon dioxide feature grabbed me,” said Zafar Rustamkulov, a graduate student at Johns Hopkins University and member of the JWST Transiting Exoplanet Community Early Release Science team, which undertook this investigation. “It was a special moment, crossing an important threshold in exoplanet sciences.”

No observatory before has ever measured such subtle differences in brightness of so many individual colors across the 3 to 5.5-micron range in an exoplanet transmission spectrum. Access to this part of the spectrum is crucial for measuring the abundances of gases like water and methane, as well as carbon dioxide. These are gases that are thought to exist in many different types of exoplanets.

“Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets,” said Natalie Batalha of the University of California at Santa Cruz, who leads the team.

Understanding the composition of a planet’s atmosphere is essential because it tells us something about the origin of the planet and how it evolved. “Carbon dioxide molecules are sensitive tracers of the story of planet formation,” said Mike Line of Arizona State University, another member of this research team. “By measuring this carbon dioxide feature, we can determine how much solid versus how much gaseous material was used to form this gas giant planet. In the coming decade, JWST will make this measurement for a variety of planets, providing insight into the details of how planets form and the uniqueness of our own solar system.”

Early Release Science

This NIRSpec prism observation of WASP-39 b is just one part of a larger investigation that includes observations of the planet using multiple Webb instruments, as well as observations of two other transiting planets. The investigation, which is part of the Early Release Science program, was designed to provide the exoplanet research community with robust Webb data as soon as possible.

“The goal is to analyze the Early Release Science observations quickly and develop open-source tools for the science community to use,” explained Vivien Parmentier, a co-investigator from Oxford University. “This enables contributions from all over the world and ensures that the best possible science will come out of the coming decades of observations.”

Natasha Batalha, co-author on the paper from NASA’s Ames Research Center, adds that “NASA’s open science guiding principles are centered in our Early Release Science work, supporting an inclusive, transparent, and collaborative scientific process.”

Reference: “Identification of carbon dioxide in an exoplanet atmosphere” by The JWST Transiting Exoplanet Community Early Release Science Team: Eva-Maria Ahrer, Lili Alderson, Natalie M. Batalha, Natasha E. Batalha, Jacob L. Bean, Thomas G. Beatty, Taylor J. Bell, Björn Benneke, Zachory K. Berta-Thompson, Aarynn L. Carter, Ian J. M. Crossfield, Néstor Espinoza, Adina D. Feinstein, Jonathan J. Fortney, Neale P. Gibson, Jayesh M. Goyal, Eliza M. -R. Kempton, James Kirk, Laura Kreidberg, Mercedes López-Morales, Michael R. Line, Joshua D. Lothringer, Sarah E. Moran, Sagnick Mukherjee, Kazumasa Ohno, Vivien Parmentier, Caroline Piaulet, Zafar Rustamkulov, Everett Schlawin, David K. Sing, Kevin B. Stevenson, Hannah R. Wakeford, Natalie H. Allen, Stephan M. Birkmann, Jonathan Brande, Nicolas Crouzet, Patricio E. Cubillos, Mario Damiano, Jean-Michel Désert, Peter Gao, Joseph Harrington, Renyu Hu, Sarah Kendrew, Heather A. Knutson, Pierre-Olivier Lagage, Jérémy Leconte, Monika Lendl, Ryan J. MacDonald, E. M. May, Yamila Miguel, Karan Molaverdikhani, Julianne I. Moses, Catriona Anne Murray, Molly Nehring, Nikolay K. Nikolov, D. J. M. Petit dit de la Roche, Michael Radica, Pierre-Alexis Roy, Keivan G. Stassun, Jake Taylor, William C. Waalkes, Patcharapol Wachiraphan, Luis Welbanks, Peter J. Wheatley, Keshav Aggarwal, Munazza K. Alam, Agnibha Banerjee, Joanna K. Barstow, Jasmina Blecic, S. L. Casewell, Quentin Changeat, K. L. Chubb, Knicole D. Colón, Louis-Philippe Coulombe, Tansu Daylan, Miguel de Val-Borro, Leen Decin, Leonardo A. Dos Santos, Laura Flagg, Kevin France, Guangwei Fu, A. García Muñoz, John E. Gizis, Ana Glidden, David Grant, Kevin Heng, Thomas Henning, Yu-Cian Hong, Julie Inglis, Nicolas Iro, Tiffany Kataria, Thaddeus D. Komacek, Jessica E. Krick, Elspeth K.H. Lee, Nikole K. Lewis, Jorge Lillo-Box, Jacob Lustig-Yaeger, Luigi Mancini, Avi M. Mandell, Megan Mansfield, Mark S. Marley, Thomas Mikal-Evans, Giuseppe Morello, Matthew C. Nixon, Kevin Ortiz Ceballos, Anjali A. A. Piette, Diana Powell, Benjamin V. Rackham, Lakeisha Ramos-Rosado, Emily Rauscher, Seth Redfield, Laura K. Rogers, Michael T. Roman, Gael M. Roudier, Nicholas Scarsdale, Evgenya L. Shkolnik, John Southworth, Jessica J. Spake, Maria E Steinrueck, Xianyu Tan, Johanna K. Teske, Pascal Tremblin, Shang-Min Tsai, Gregory S. Tucker, Jake D. Turner, Jeff A. Valenti, Olivia Venot, Ingo P. Waldmann, Nicole L. Wallack, Xi Zhang and Sebastian Zieba, Accepted, Nature.
arXiv:2208.11692

The James Webb Space Telescope is the world’s premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.