The James Webb Space Telescope has just obtained another first: a detailed molecular and chemical portrait of the skies of a distant world.
The James Webb Space Telescope (JWST) is proving to be such a powerful instrument that a week goes by without a startling new image. On this occasion, he captured the atmosphere of a “hot Saturn”, a Saturn-mass planet orbiting a star about 700 light-years away. The planet is known as WASP-39 b.
Previously, other space telescopes, such as Hubble and Spitzer, had taken pictures of this boiling planet’s atmosphere and revealed some of its components. However, the new readings by James Webb provide a complete list of atoms, molecules and even signs of active chemistry and clouds.
Spanish astrophysicist Mercedes López Morales, of the Harvard and Smithsonian Center for Astrophysics, is one of the scientists who contributed to the new results. “We had predicted that we would see a lot of these signals, but even so, when I first saw the data, I was blown away,” she said.
These latest data also provide a clue to what these clouds on exoplanets might look like when seen up close: fragmented rather than a single, uniform mantle over the planet. These images indicate that with JWST it will be possible to explore the atmospheres of smaller rocky planets, such as those in the TRAPPIST-1 system.
All these discoveries appear in a set of five scientific articles available on the arXiv prepress site. Among the revelations is the first detection in an exoplanet’s atmosphere of sulfur dioxide, a molecule produced by chemical reactions triggered by high-energy light from the star around which the planet orbits. On Earth, the upper atmosphere’s protective ozone layer is created in a similar way.
The surprising detection of sulfur dioxide finally confirms that photochemistry, the interaction between light and atmospheric components, determines the climate of “hot Saturns”. Earth’s climate is also determined by photochemistry, so our planet has more in common with these exoplanets than we previously knew.
The exoplanet WASP-39 b has an estimated surface temperature of 870ºC, and the atmosphere is mainly composed of hydrogen, which does not exactly make it habitable. The exoplanet has been compared to both Saturn and Jupiter, with a mass similar to Saturn’s but an overall size as large as Jupiter’s because it is less dense.
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. A better understanding of the star-planet connection should lead to a better understanding of how these processes create the observed diversity of planets in the galaxy.
JWST also saw carbon dioxide at higher resolution, providing twice the data reported in its previous observations. On the other hand, carbon monoxide was detected, but the data showed no obvious signs of methane or hydrogen sulfide. If present, these molecules are at very low levels. This wealth of data was obtained thanks to the fact that the JWST observes the universe in infrared light and allows it to capture chemical signatures that cannot be detected in visible light.
To see WASP-39 b’s light, JWST tracked the planet as it passed in front of its star, allowing some of the starlight 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.
REFERENCE
Early launch science of exoplanet WASP-39b with JWST NIRSpec G395H