The James Webb Space Telescope (JWST) has already delivered fascinating pictures from the depths of space. Now it reveals for the first time an abundance of information about a planet that is around 700 light years away from our earth. The exoplanet called WASP-39B was discovered in 2011, but has never been examined so much. The planet is a gas giant like Jupiter, but has only about a third of its mass and rather resembles Saturn in its composition. He circles a sun -like star on just four earth days and is much closer to him than Mercury of our sun. With a temperature of around 900 degrees Celsius and extreme brightness, it is therefore too inhospitable for life as we know it.
Already at the beginning of the year, astronomers were able to prove with the help of the JWST that carbon dioxide is hidden in the atmosphere of the exoplanet. This is the first time that this gas has been observed on an exoplanet. Now the space telescope has identified even more elements and chemical compounds: sodium, potassium, water, sulfur dioxide and carbon monoxide. The presence of sulfur dioxide suggests that a photochemical reaction takes place in the atmosphere when the star's light hits it – similar to how our Sun creates ozone from the oxygen in the Earth's atmosphere. In the case of WASP-39b, the light of its star in the atmosphere splits water into atomic hydrogen and hydroxyl radicals. The resulting radicals, in turn, react with hydrogen sulfide, so that sulfur dioxide is formed.
"Because photochemistry is such an important process here on Earth, it's likely important on other potentially habitable planets as well," explains Jacob Bean, an astronomer at the University of Chicago in Illinois and co-leader of the observing team. "Until now, we have 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."
The observations of JWST also showed a relatively low ratio of carbon to oxygen on the planet. This indicates that WASP-39B used to absorb a lot of water in the form of ice. The researchers suspect that the gas giant has formed much further outside in its star system and only later got into its current close orbit. However, it is unclear whether it is a slow process that might have dragged on for several million years, or a faster process that was triggered by a gravitational trigger by another planet or neighboring star.
The astronomers were also able to observe another phenomenon that has not yet been detected in any exoplanet: the planet has an incomplete cloud cover. At the border between day and night, the planet is only about 60 percent covered by clouds. According to Jacob Bean, this may be due to the clouds evaporating when they reach the hotter side of the day and condensing when they reach the cooler night side.
The fascinating findings on WASP-39b raise expectations for further future discoveries on other planets. The JWST will observe 70 more exoplanets in its first year.
