New observations from WASP-39 b reveal, among other things, a never-before-seen molecule in a planet’s atmosphere, sulfur dioxide.
The telescope’s highly sensitive instruments were trained on the atmosphere of a “hot Saturn” — a planet about as massive as Saturn and orbiting a star some 700 light-years away — known as WASP-39 b. While JWST and other space telescopes, including Hubble and Spitzer, have previously revealed isolated components of this seething planet’s atmosphere, the new readings offer 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 Lopez-Morales, astronomer at the Center for Astrophysics | Harvard & Smithsonian and one of the scientists who contributed to the new results.
“We had predicted that we would see many of these signals, but when I first saw the data, I was impressed,” adds Lopez-Morales.
The latest data also gives a hint of what these clouds might look like on exoplanets up close: broken rather than a single, uniform blanket over the planet.
The results bode well for the JWST’s ability to conduct the wide range of studies of exoplanets – planets around other stars – that scientists had hoped for. This includes studying the atmospheres of smaller rocky planets like those in the TRAPPIST-1 system.
“We observed the exoplanet with multiple instruments, which together provide a wide range of infrared spectra and a range of chemical fingerprints that were inaccessible until the JWST,” said Natalie Batalha, an astronomer at the University of California, Santa Cruz, who contributed to and has helped coordinate the new research. “Data like this is a game changer.”
The series of discoveries are detailed in a series of five newly submitted papers available on the arXiv preprint website. Among the unprecedented revelations is the first detection of sulfur dioxide in an exoplanet’s atmosphere, a molecule formed by chemical reactions triggered by high-energy light from the planet’s parent star. Similarly, on Earth, the protective ozone layer forms in the upper atmosphere.
“The surprising detection of sulfur dioxide finally confirms that photochemistry shapes the climate of ‘hot Saturns,'” said Diana Powell, NASA Hubble Fellow, astronomer at the Center for Astrophysics and core member of the team that made the sulfur dioxide discovery. “Earth’s climate is also shaped by photochemistry, so our planet has more in common with ‘hot Saturns’ than we previously knew!”
Jea Adams, a Harvard graduate student and researcher at the Center for Astrophysics, analyzed the data that confirmed the sulfur dioxide signal.
“As a young researcher in the field of exoplanet atmospheres, it’s so exciting to be a part of a discovery like this,” says Adams. “The process of analyzing this data felt magical. We saw evidence of this feature in early data, but this higher precision instrument clearly showed the signature of SO2 and helped us solve the mystery.”
With an estimated temperature of 1,600 degrees Fahrenheit and an atmosphere composed mostly of hydrogen, WASP-39 b is believed to be unhabitable. The exoplanet has been compared to both Saturn and Jupiter, with a similar mass to Saturn but an overall size as large as Jupiter. But the new work points the way to finding evidence of potential life on a habitable planet.
The planet’s proximity to its parent star – eight times closer than Mercury is to our Sun – also makes it a laboratory for studying the effects of parent star radiation on exoplanets. A better knowledge of the star-planet connection should bring a deeper understanding of how these processes produce the diversity of planets observed in the galaxy.
Other atmospheric constituents discovered by JWST include sodium, potassium and water vapor, confirming previous spaceborne and ground-based telescopic observations and discovering additional water features at longer wavelengths not previously seen.
JWST also saw carbon dioxide with higher resolution, providing twice as much data as previous observations. Meanwhile, carbon monoxide was detected, but obvious signatures of methane and hydrogen sulfide were missing from the data. When present, these molecules occur in very small amounts, a significant finding for scientists compiling inventories of exoplanet chemistry to better understand the formation and evolution of these distant worlds.
Capturing such a broad spectrum of WASP-39b’s atmosphere was a scientific tour de force, as an international team independently analyzed data from four of JWST’s finely calibrated instrument modes with hundreds of data sets. They then performed detailed comparisons of their findings, which yielded even more scientifically nuanced results.
JWST views the universe in infrared light, at the red end of the light spectrum beyond what the human eye can see; This allows the telescope to pick up chemical fingerprints that cannot be seen in visible light.
Each of the three instruments even has a version of the “IR” of infrared in its name: NIRSpec, NIRCam, and NIRISS.
To see light from WASP-39 b, JWST tracked the planet as it passed in front of its star and allowed 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 missing colors tell astronomers which molecules are present.
By analyzing an exoplanet atmosphere with such precision, the JWST instruments have far exceeded scientists’ expectations – and promise a new phase in the exploration of the galaxy’s wide variety of exoplanets.
Lopez-Morales says: “I look forward to seeing what we find in the atmospheres of small terrestrial planets.
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