Le télescope spatial Webb détecte du dioxyde de carbone dans l’atmosphère d’une exoplanète

Exoplanète WASP-39 b et son étoile (illustration)

Cette illustration montre à quoi pourrait ressembler l’exoplanète WASP-39 b en fonction de la compréhension actuelle de la planète.
WASP-39b est une géante gazeuse chaude et gonflée avec une masse de 0,28 fois Jupiter (0,94 fois Saturne) et un diamètre 1,3 fois celui de Jupiter, mesurant seulement 0,0486 unités astronomiques (4 500 000 miles) en orbite autour de son étoile. L’étoile WASP-39 est légèrement plus petite et moins massive que le Soleil. Parce qu’il est si proche de son étoile, WASP-39 b est très chaud et susceptible d’être capturé par les marées, avec un côté toujours face à l’étoile. Les données recueillies par le spectrographe proche infrarouge de Webb (NIRSpec) montrent clairement la présence de dioxyde de carbone dans l’atmosphère, tandis que les observations précédentes des télescopes spatiaux Hubble et Spitzer de la NASA et d’autres télescopes indiquent la présence de vapeur d’eau, de sodium et de potassium. La planète est susceptible d’avoir des nuages ​​et une certaine forme de temps, mais elle peut ne pas avoir de bandes atmosphériques comme celles de Jupiter et de Saturne. Crédits photo : NASA, ESA, ASC, Joseph Olmsted (STScI)

Le Webbus de la NASA annonce une nouvelle ère dans la recherche sur les exoplanètes avec la première détection définitive de dioxyde de carbone dans l’atmosphère d’une planète en dehors de notre système solaire.

Après des années de préparation et d’anticipation,[{” attribute=””>exoplanet scientists are overjoyed. NASA’s James Webb Space Telescope has captured an astonishingly detailed rainbow of near-infrared starlight filtered through the atmosphere of a hot gas giant exoplanet 700 light-years away. The transmission spectrum of exoplanet WASP-39 b, based on a single set of measurements made using Webb’s Near-Infrared Spectrograph and analyzed by dozens of researchers, represents a hat trick of firsts: Webb’s first official scientific observation of an exoplanet; the first detailed exoplanet spectrum covering this range of near-infrared colors; and the first indisputable evidence for carbon dioxide in the atmosphere of a planet orbiting a distant star. The results are indicative of Webb’s ability to spot key molecules like carbon dioxide in a wide variety of exoplanets – including smaller, cooler, rocky planets. This shows it is capable of providing insights into the composition, formation, and evolution of planets across the galaxy.


Regardez cet épisode de Space Sparks pour en savoir plus sur la façon dont le télescope spatial James Webb a trouvé des preuves claires de dioxyde de carbone dans l’atmosphère d’une planète géante gazeuse en orbite autour d’une étoile semblable au Soleil à 700 années-lumière.

Webb de la NASA détecte du dioxyde de carbone dans l’atmosphère d’une exoplanète

Le télescope spatial James Webb de la NASA a effectué la première détection définitive de dioxyde de carbone dans l’atmosphère d’un exoplanète – une planète hors du système solaire. Cette observation d’une planète géante gazeuse en orbite autour d’une étoile semblable au Soleil à 700 années-lumière de la Terre fournit des informations importantes sur la composition et la formation de la planète. La découverte acceptée pour publication dans la revue La naturefournit la preuve que Webb pourrait à l’avenir être en mesure de détecter et de mesurer le dioxyde de carbone dans les atmosphères plus minces de planètes rocheuses plus petites.

L’exoplanète WASP-39 b est une géante à gaz chaud d’une masse d’environ un quart de la masse[{” attribute=””>Jupiter (about the same as Saturn) and a diameter 1.3 times greater than Jupiter. Its extreme puffiness is related in part to its high temperature (about 1,600 degrees Fahrenheit or 900 degrees Celsius). Unlike the cooler, more compact gas giants in our solar system, WASP-39 b orbits very close to its star. In fact, it is only about one-eighth the distance between the Sun and Mercury and completes one circuit in just over four Earth-days. The planet’s discovery, reported in 2011, was made based on ground-based detections of the subtle, periodic dimming of light from its host star as the planet transits, or passes in front of the star.

Previous observations from other telescopes, including NASA’s Hubble and Spitzer space telescopes, revealed the planet’s atmosphere contained water vapor, sodium, and potassium. Webb’s unmatched infrared sensitivity has now confirmed the presence of carbon dioxide on this exoplanet as well.

Exoplanet WASP-39 b (NIRSpec Transmission Spectrum)

A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by Webb’s Near-Infrared Spectrograph (NIRSpec) on July 10, 2022, reveals the first clear evidence for carbon dioxide in a planet outside the solar system. This is also the first detailed exoplanet transmission spectrum ever captured that covers wavelengths between 3 and 5.5 microns.
A transmission spectrum is made by comparing starlight filtered through a planet’s atmosphere as it moves in front of the star, to the unfiltered starlight detected when the planet is beside the star. Each of the 95 data points (white circles) on this graph represents the amount of a specific wavelength of light that is blocked by the planet and absorbed by its atmosphere. Wavelengths that are preferentially absorbed by the atmosphere appear as peaks in the transmission spectrum. The peak centered around 4.3 microns represents the light absorbed by carbon dioxide.
The gray lines extending above and below each data point are error bars that show the uncertainty of each measurement, or the reasonable range of actual possible values. For a single observation, the error on these measurements is extremely small.
The blue line is a best-fit model that takes into account the data, the known properties of WASP-39 b and its star (e.g., size, mass, temperature), and assumed characteristics of the atmosphere. Researchers can vary the parameters in the model – changing unknown characteristics like cloud height in the atmosphere and abundances of various gases – to get a better fit and further understand what the atmosphere is really like. The model shown here assumes that the planet is made primarily of hydrogen and helium, with small amounts of water and carbon dioxide, and a thin veil of clouds.
The 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 measuring the brightness of each wavelength at set intervals of time.
Credit: NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI)

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.

Exoplanet WASP-39 b (NIRSpec Transit Light Curves)

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.

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