Four highly sensitive instruments on the James Webb Space Telescope (JWST) were trained on the atmosphere of a hot Saturn – a planet about as massive as Saturn orbiting a star 700 light-years away known as WASP-39 b, revealing an unprecedented view into a chemical portrait of the planet’s skies, a team of scientists from institutions worldwide and NYU Abu Dhabi (NYUAD) reported.
While previous observations detected 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, highlights Jasmina Blecic, a scientist at NYUAD’s Center for Astro, Particle and Planetary Physics (CAP3), a member of the only Exoplanetary Atmospheres research group in UAE led by Ian Dobbs-Dixon, and part of the JWST team.
JWST sees the universe in infrared light, on the red end of the light spectrum beyond what human eyes can see. This allows the telescope to pick up fingerprints of molecular species that cannot be detected in visible light. WASP-39 b was observed as it passed in front of its host star, capturing in this way the starlight filtered through the planetary atmosphere. Different molecular species present in the planetary atmosphere absorbed different parts of the stellar light, revealing the enriched chemical background of the planet envelope.
“The clarity of the observations which came from these instruments, before any data cleaning was performed, was mind blowing!” says Blecic. “The raw data looked polished, as if we already performed a heavy lifting of reducing noise and instrumental errors that we used to do with the Spitzer and Hubble telescopes, and the molecular features were noticeable from a first look,” says Blecic. These facts bode well for the capabilities of the JWST instruments to conduct investigations of smaller, rocky exoplanets, hoped for by the science team.
The suite of new discoveries is detailed in a set of five new scientific papers co-authored by Blecic, to be published this month in the journal Nature. Among the remarkable revelations is the first detection of sulfur dioxide in an exoplanet atmosphere, a molecule produced from chemical reactions triggered by high-energy photons coming from the planet’s star. On Earth, the protective ozone layer is created in a similar way.
“This is the first time we see concrete evidence of photochemistry on exoplanets,” said Shang-Min Tsai, a researcher at the University of Oxford and the author of the paper explaining the origin of sulfur dioxide in WASP-39 b’s atmosphere. “It is also the first time that we had to include higher level physics into our models so we can explain the data,” adds Blecic. The resulting improvements in modeling will help interpret potential signs of life in the future, when we observe smaller, potentially habitable, terrestrial-sized planets. With an estimated temperature of 1,600 degrees Fahrenheit (900 degrees Celsius) and an atmosphere made mostly of hydrogen, WASP-39 b is, however, not believed to be habitable.
Other atmospheric constituents detected by JWST include sodium, potassium, and water vapor, confirming previous observations, as well as additional water features, at longer wavelengths, that have not been seen before.
“We, again, saw, and now confirmed with multiple JWST instruments, carbon dioxide,” emphasizes Blecic. “Carbon dioxide is ubiquitous in our solar system. It is also the most abundant chemical species in the atmospheres of terrestrial, but inhabitable planets like Venus and Mars, both sitting, together with Earth, within the boundaries of our Sun’s habitable zone. This first indisputable detection of this molecule in an exoplanetary atmosphere has, thus, opened new frontiers for future JWST observations of planets laying within the habitable zones of their host stars, as it will allow us to differentiate between habitable and inhabitable worlds,” Blecic said.
The latest data also give us a hint of how clouds on WASP-39 b might look up close: a patchy, broken up cloud structure like on Earth, rather than a single, uniform blanket across the planet as we see on Venus.
Having such a complete roster of ingredients in an exoplanet atmosphere also gives scientists a glimpse of how this planet, and perhaps others, formed. WASP-39 b’s chemical inventory suggests its formation far away from its host star, and a history of smashups and mergers of smaller bodies called planetesimals that eventually created a goliath of a planet.
Capturing such a broad spectrum of WASP-39 b’s atmosphere was a scientific tour de force. The international team was numbering hundreds of independently analyzed data, performing at the same time detailed inter-comparisons of their findings, yielding yet more scientific results.
“These magnificent discoveries, disclosed from the observation of a single target, demonstrated performance of the JWST instruments well beyond scientists’ expectations, establishing an exciting path for future observations, and opening a new era of exploration among the huge diversity of exoplanets within our galaxy,” concludes Blecic.
The five papers featured in this research include: