Revealing The Atmosphere Of An Exoplanet

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). Image credit: Credits: NASA, ESA, CSA, J. Olmsted (STScI)

New readings from the James Webb Space Telescope are providing a full menu of atoms, molecules, and even signs of active chemistry and clouds.

The telescope’s array of highly sensitive instruments was trained on the atmosphere of WASP-39 b, a “hot Saturn” (a planet about as massive as Saturn but in an orbit tighter than Mercury) orbiting a star some 700 light-years away.

Commenting Natalie Batalha, an astronomer at the University of California, Santa Cruz, who contributed to and helped coordinate the new research, said:

“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.”

The planet’s proximity to its host star – eight times closer than Mercury is to our Sun – also makes it a laboratory for studying the effects of radiation from host stars on exoplanets. Better knowledge of the star-planet connection should bring a deeper understanding of how these processes affect the diversity of planets observed in the galaxy.

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 viewing the universe in infrared light, Webb can pick up chemical fingerprints that can’t be detected in visible light.

Other atmospheric constituents detected by the Webb telescope include sodium (Na), potassium (K), and water vapor (H2O), confirming previous space and ground-based telescope observations as well as finding additional fingerprints of water, at these longer wavelengths, that haven’t been seen before.

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

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

The observations and data calculations involved an international team.

“We are going to be able to see the big picture of exoplanet atmospheres,” said Laura Flagg, a researcher at Cornell University and a member of the international team.

“It is incredibly exciting to know that everything is going to be rewritten. That is one of the best parts of being a scientist.”

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