Exoplanet WASP-39 b Illustration

New molecule: Webb reveals an exoplanet atmosphere “Hot Saturn”

Exoplanet WASP-39b Illustration

This illustration represents the exoplanet WASP-39b and its star. Credit: Melissa Weiss/Center for Astrophysics | Harvard and Smithsonian

New Webb Space Telescope observations of WASP-39b reveal a molecule never before seen in a planet’s atmosphere – sulfur dioxide – among other details.

The telescope’s highly sensitive instrument array was trained on the atmosphere of WASP-39b, a “

Saturn is the sixth planet from the sun and has the second largest mass in the solar system. It has a much lower density than Earth but a much larger volume. Saturn’s name comes from the Roman god of wealth and agriculture.

” data-gt-translate-attributes=”[{” attribute=””>Saturn” located around 700 light-years away. A hot Saturn is an exoplanet that is about as massive as Saturn and orbits closely to a star such that it has high surface-atmosphere temperatures. Although Webb and other space telescopes, including Hubble and Spitzer, have previously revealed isolated ingredients of this broiling planet’s atmosphere, the new readings provide a full menu of atoms, molecules, and even signs of active chemistry and clouds.

“The clarity of the signals from a number of different molecules in the data is remarkable,” says Mercedes López-Morales, an astronomer at the Center for Astrophysics | Harvard & Smithsonian and one of the scientists who contributed to the new results.

“We had predicted that we were going to see many of those signals, but still, when I first saw the data, I was in awe,” López-Morales adds.

The latest data also give a hint of how these clouds in exoplanets might look up close: broken up rather than a single, uniform blanket over the planet.

The findings bode well for the capability of Webb to conduct the broad range of investigations on exoplanets — planets around other stars — scientists hoped for. That includes probing the atmospheres of smaller, rocky planets like those in the TRAPPIST-1 system.

“We observed the Exoplanet WASP-39 b Sulfur Dioxide

Webb Space Telescope observations of WASP-39 b reveal sulfur dioxide in the atmosphere. This is the first time this has been detected in the atmosphere of an exoplanet. Credit: Melissa Weiss/Center for Astrophysics | Harvard & Smithsonian

The suite of discoveries is detailed in a set of five new submitted scientific papers, available on the preprint server arXiv. Among the unprecedented revelations is the first detection in an exoplanet atmosphere of sulfur dioxide, a molecule produced from chemical reactions triggered by high-energy light from the planet’s parent star. On Earth, the protective ozone layer in the upper atmosphere is created in a similar way.

“The surprising detection of sulfur dioxide finally confirms that photochemistry shapes the climate of hot Saturns,’” says Diana Powell, a Exoplanet WASP-39 b (Webb Transmission Spectra)

The atmospheric composition of the hot gas giant exoplanet WASP-39 b has been revealed by NASA’s James Webb Space Telescope. This graphic shows four transmission spectra from three of Webb’s instruments operated in four instrument modes. At upper left, data from NIRISS shows fingerprints of potassium (K), water (H2O), and carbon monoxide (CO). At upper right, data from NIRCam shows a prominent water signature. At lower left, data from NIRSpec indicates water, sulfur dioxide (SO2), carbon dioxide (CO2), and carbon monoxide (CO). At lower right, additional NIRSpec data reveals all of these molecules as well as sodium (Na). Credit: NASA, ESA, CSA, Joseph Olmsted (STScI)

At an estimated temperature of 1,600 degrees

Each of the three instruments even has some version of the “IR” of infrared in its name: NIRSpec, NIRCam, and NIRISS.

To see light from WASP-39 b, Webb tracked the planet as it passed in front of its star, allowing some of the star’s light to filter through the planet’s atmosphere. Different types of chemicals in the atmosphere absorb different colors of the starlight spectrum, so the colors that are missing tell astronomers which molecules are present.

By so precisely parsing an exoplanet atmosphere, the Webb instruments performed well beyond scientists’ expectations — and promise a new phase of exploration among the broad variety of exoplanets in the galaxy.

López-Morales says, “I am looking forward to seeing what we find in the atmospheres of small, terrestrial planets.”

For more on this topic, see NASA’s Webb Reveals an Exoplanet Unlike Any in Our Solar System.

Reference: “Direct Evidence of Photochemistry in an Exoplanet Atmosphere” by Shang-Min Tsai, Elspeth K. H. Lee, Diana Powell, Peter Gao, Xi Zhang, Julianne Moses, Eric Hébrard, Olivia Venot, Vivien Parmentier, Sean Jordan, Renyu Hu, Munazza K. Alam, Lili Alderson, Natalie M. Batalha, Jacob L. Bean, Björn Benneke, Carver J. Bierson, Ryan P. Brady, Ludmila Carone, Aarynn L. Carter, Katy L. Chubb, Julie Inglis, Jérémy Leconte, Mercedes Lopez-Morales, Yamila Miguel, Karan Molaverdikhani, Zafar Rustamkulov, David K. Sing, Kevin B. Stevenson, Hannah R Wakeford, Jeehyun Yang, Keshav Aggarwal, Robin Baeyens, Saugata Barat, Miguel de Val Borro, Tansu Daylan, Jonathan J. Fortney, Kevin France, Jayesh M Goyal, David Grant, James Kirk, Laura Kreidberg, Amy Louca, Sarah E. Moran, Sagnick Mukherjee, Evert Nasedkin, Kazumasa Ohno, Benjamin V. Rackham, Seth Redfield, Jake Taylor, Pascal Tremblin, Channon Visscher, Nicole L. Wallack, Luis Welbanks, Allison Youngblood, Eva-Maria Ahrer, Natasha E. Batalha, Patrick Behr, Zachory K. Berta-Thompson, Jasmina Blecic, S.L. Casewell, Ian J.M. Crossfield, Nicolas Crouzet, Patricio E. Cubillos, Leen Decin, Jean-Michel Désert, Adina D. Feinstein, Neale P. Gibson, Joseph Harrington, Keivn Heng, Thomas Henning, Eliza M.-R. Kempton, Jessica Krick, Pierre-Olivier Lagage, Monika Lendl, Michael Line, Joshua D. Lothringer, Megan Mansfield, N. J. Mayne, Thomas Mikal-Evans, Enric Palle, Everett Schlawin, Oliver Shorttle, Peter J. Wheatley and Sergei N. Yurchenko, 18 November 2022, Astrophysics > Earth and Planetary Astrophysics.

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