https://www.nature.com/articles/d41586-022-03820-3 Skip to main content Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Advertisement Advertisement Nature * View all journals * Search * My Account Login * Explore content * About the journal * Publish with us * Subscribe * Sign up for alerts * RSS feed 1. nature 2. news 3. article * NEWS * 22 November 2022 * Update 23 November 2022 First active chemistry on an exoplanet revealed by Webb telescope Ground-breaking observations reveal clouds, chemical reactions and more on a world outside our Solar System. * Jonathan O'Callaghan 1. Jonathan O'Callaghan View author publications You can also search for this author in PubMed Google Scholar * Twitter * Facebook * Email You have full access to this article via your institution. Download PDF An illustration of the exoplanet (extrasolar planet) Wasp-39b, also called a "hot Saturn." The exoplanet WASP-39b (artist's impression) is similar in composition to Saturn.Credit: Science Photo Library/Alamy The James Webb Space Telescope (JWST) has produced the most detailed information ever on an exoplanet, making it the world we know most about after the eight major planets of our Solar System. Observations of the planet, called WASP-39b, reveal patchy clouds, an intriguing chemical reaction in its atmosphere, and provide hints about its formation. "We've studied lots of planets before," says Laura Kreidberg, director of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and part of the observation team, which posted five papers^1^,^2^,^3^,^4^,^5 on their observations on the arXiv preprint server on 22 November. "But we've never seen a data set like this." [d41586-022] The $11-billion Webb telescope aims to probe the early Universe WASP-39b is a 'hot Jupiter' located 215 parsecs (700 light-years) from Earth. The gas giant is about one-third the mass of Jupiter and more similar in composition to Saturn. It orbits its host star in just four Earth days and is eight times closer to it than Mercury is to our Sun, making it incredibly hot at nearly 900oC. This proximity and its consequent brightness makes the planet inhospitable to life as we know it, but made it the "perfect target" for JWST to observe early in its life and test its exoplanet capabilities, says Kreidberg. JWST, launched in December 2021, observed the planet for more than 40 hours in July. Initial results showed carbon dioxide in the planet's atmosphere, the first time the gas had been seen on an exoplanet. Surprise chemistry Using three of its instruments, JWST was able to observe light from the planet's star as it filtered through WASP-39b's atmosphere, a process known as transmission spectroscopy. This allowed a team of more than 300 astronomers to detect water, carbon monoxide, sodium, potassium and more in the planet's atmosphere, in addition to the carbon dioxide. The gives the planet a similar composition to Saturn, although it has no detectable rings. The team were also surprised to detect sulfur dioxide, which had appeared as a mysterious bump in early observation data. Its presence suggests a photochemical reaction is taking place in the atmosphere as light from the star hits it, similar to how our Sun produces ozone in Earth's atmosphere. In WASP-39b's case, light from its star, slightly smaller than the Sun, splits water in its atmosphere into hydrogen and hydroxide, which reacts with hydrogen sulfide to produce sulfur dioxide. "These spectra are just exquisite in their detail, and reveal an additional way that the star affects the planet's atmospheric composition, through photochemistry," says Victoria Meadows, astronomer at the University of Washington in Seattle. "Photochemistry, because it is such an important process here on Earth, is probably an important process on other potentially habitable planets," says Jacob Bean, an astronomer at the University of Chicago in Illinois and the observation team's co-leader. Until now, "we've only been able to test our understanding of photochemistry in our Solar System. But planets around other stars give us access to completely different physical conditions". [d41586-022] Landmark Webb telescope releases first science image -- astronomers are in awe Planetary migration The results also showed a relatively low ratio of carbon to oxygen on the planet. This suggests that WASP-39b previously absorbed a high amount of water as ice, probably when it was in a different position, and suggests that it formed much farther out in its solar system, perhaps comparable to "where Jupiter is" around our Sun, says Eva-Maria Ahrer, an astronomer at the University of Warwick, UK, and lead author on one of the papers. Such migration of hot Jupiters is expected, to explain their proximity to their stars. What remains unclear is if this is a slow process over perhaps tens of millions of years, or a faster process resulting from a gravitational 'shove' from another planet or star. Knowing WASP-39b's composition could help astronomers to determine which scenario occurred. The observations also show the planet -- which is tidally locked to its star, so the same face always points towards it because of the immense gravitational attraction -- has incomplete cloud cover, something astronomers have never observed before on an exoplanet. At the boundary of night and day, the planet is "only about 60% is covered by clouds", says Bean, perhaps caused by clouds evaporating as they reach the hotter day side and condensing as they reach the cooler night. [d41586-022] Webb telescope spots CO2 on exoplanet for first time: what it means for finding alien life Benchmark planet JWST is observing some 70 exoplanets in its first year of science, which began in July and will run until next June. WASP-39b provides a "benchmark" for those studies, says Bean. That includes planets in the TRAPPIST-1 system, where a small red dwarf star is orbited by seven Earth-sized worlds, some of which could be revealed to be potentially habitable by transmission spectroscopy. "This shows that, when it comes to delving into exoplanetary atmospheres, JWST is every bit as powerful as we hoped," says Hugh Osborn, exoplanet scientist at the University of Bern in Switzerland. In December, meanwhile, the telescope will watch a planet called WASP-43b complete an entire orbit around its star, lasting one Earth day, revealing unprecedented details in the planet's climate and chemistry. "We think this planet may have very thick clouds on its night side," says Kreidberg. "We hope to determine what the clouds are made out of. It will be really spectacular." doi: https://doi.org/10.1038/d41586-022-03820-3 Updates & Corrections * Update 23 November 2022: This story has been updated with quotes from Victoria Meadows and Hugh Osborn. References 1. Rustamkulov, Z. et al. Preprint at arXiv https://doi.org/10.48550 /arXiv.2211.10487 (2022). 2. Alderson, L. et al. Preprint at arXiv https://doi.org/10.48550/ arXiv.2211.10488 (2022). 3. Ahrer, E.-M. et al. Preprint at arXiv https://doi.org/10.48550/ arXiv.2211.10489 (2022). 4. Tsai, S.-M. et al. Preprint at arXiv https://doi.org/10.48550/ arXiv.2211.10490 (2022). 5. Feinstein, A. D. et al. Preprint at arXiv https://doi.org/ 10.48550/arXiv.2211.10493 (2022). 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