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Webb Reveals Atmospheric Composition of Hot-Saturn WASP-39b

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While the NASA/ESA/CSA James Webb Space Telescope and other space telescopes previously have revealed isolated ingredients of the atmosphere of WASP-39b, a hot-Saturn exoplanet orbiting a star some 700 light-years away, the new findings provide a full menu of atoms, molecules, and even signs of active chemistry and clouds. The results will appear in a set of five papers in the journal Nature.

This illustration shows what WASP-39b could look like, based on the current understanding of the planet. Image credit: NASA / ESA / CSA / Webb / J. Olmsted, STScI.

WASP-39b is a hot gas giant that orbits the G7-type star WASP-39 with a period of 4.1 days.

First discovered in 2011, the alien world has approximately the same mass as Saturn but is 50% larger.

The planet’s extreme puffiness is related in part to its high temperature (about 900 degrees Celsius, or 1,652 degrees Fahrenheit).

“We observed the exoplanet with multiple instruments that, together, provide a broad swath of the infrared spectrum and a panoply of chemical fingerprints inaccessible until this mission. Data like these are a game changer,” said Dr. Natalie Batalha, an astronomer at the University of California, Santa Cruz.

To see light from WASP-39b, 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.

Among the unprecedented revelations is the first detection in an exoplanet atmosphere of sulfur dioxide (SO2), 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.

This graphic shows four transmission spectra of WASP-39b from three of Webb’s instruments operated in four instrument modes. All are plotted on a common scale extending from 0.5 to 5.5 microns. 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). Image credit: NASA / ESA / CSA / Webb / J. Olmsted, STScI.

“This is the first time we see concrete evidence of photochemistry — chemical reactions initiated by energetic stellar light — on exoplanets,” said Dr. Shang-Min Tsai, a researcher at the University of Oxford.

“I see this as a really promising outlook for advancing our understanding of exoplanet atmospheres with this mission.”

Webb also detected sodium (Na), potassium (K), and water vapor (H2O), confirming previous space and ground-based telescope observations as well as finding additional fingerprints of water.

The telescope also saw carbon dioxide (CO2) at higher resolution, providing twice as much data as reported from its previous observations.

Meanwhile, carbon monoxide (CO) was detected, but obvious signatures of both methane (CH4) and hydrogen sulfide (H2S) were absent from the Webb data. If present, these molecules occur at very low levels.

WASP-39b’s chemical inventory suggests a history of smashups and mergers of planetesimals to create an eventual goliath of a planet.

“The abundance of sulfur relative to hydrogen indicated that the planet presumably experienced significant accretion of planetesimals that can deliver these ingredients to the atmosphere,” said Dr. Kazumasa Ohno, an astronomer at the University of California, Santa Cruz.

“The data also indicate that the oxygen is a lot more abundant than the carbon in the atmosphere. This potentially indicates that WASP-39b originally formed far away from the central star.”

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Z. Rustamkulov et al. 2022. Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM. Nature, in press; arXiv: 2211.10487

Lili Alderson et al. 2022. Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H. Nature, in press; arXiv: 2211.10488

Eva-Maria Ahrer et al. 2022. Early Release Science of the exoplanet WASP-39b with JWST NIRCam. Nature, in press; arXiv: 2211.10489

Shang-Min Tsai et al. 2022. Direct Evidence of Photochemistry in an Exoplanet Atmosphere. Nature, in press; arXiv: 2211.10490

Adina D. Feinstein et al. 2022. Early Release Science of the exoplanet WASP-39b with JWST NIRISS. Nature, in press; arXiv: 2211.10493

Source : Breaking Science News

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