This will also interest you
[EN VIDÉO] Understanding the James Webb Space Telescope’s Mission in a Minute The James Webb Space Telescope, the new flagship of space observation, will be launched on December 18…
Slowly but surely, month after month, the James Webb Space Telescope is providing more and more evidence of its ability to provide details about the composition of exoplanets’ atmospheres. Of course, the ultimate goal is to find convincing biosignatures in the atmosphere of an exo-Earth, but we may have to wait decades for that to happen. This does not mean that such signatures as such will not appear before 2030. It may simply take a very long time to be reasonably certain that there are no natural abiotic processes unrelated to the existence of life capable of producing the observed signal.
One of the strategies for achieving this Holy Grail is to learn as much as possible about the atmospheres of exoplanets, even uninhabitable gas giants like hot Jupiters or mini-Neptunes.
Therefore, today we are with some interest in knowing the results of a team of European astronomers jointly led by researchers from the Institute of Astronomy of KU Leuven, the famous Belgian University of Leuven. These are observations from JWSTJWST that reveal part of the composition of the exoplanet WASP-107b’s atmosphere. The resulting spectrum shows the presence not only of water vapor molecules, but also sulfur dioxide, SO2. The presence of clouds of silicate particles, cousins of sand grains, has also been demonstrated; However, no trace of methane (CH4), and that is surprising.
A planetary atmosphere has a spectral signature that represents its chemical composition, but also its cloud and “mist” composition. Thanks to various techniques, it is possible to determine the physicochemical properties of the atmosphere of an exoplanet. These techniques include: spectroscopic transit, secondary transit or eclipse, direct spectroscopic observation of the planet, or even observation of the planet in different phases around the star to measure temporal and seasonal variations. Discover exoplanets in our 9-part web series, available on our YouTube channel. A playlist proposed by the CEA and the University of Paris-Saclay as part of the European research project H2020 Exoplanets-A. © CEA
The lack of methane poses challenges for planetary scientists
WASP-107b was observed years ago with the Hubble Telescope. In fact, we have known for some time that it is one of the lowest known density exoplanets. Although its mass is only 12% that of Jupiter, its diameter is comparable because it is strongly heated by its parent star (slightly colder and less massive than our Sun), which it orbits in just six days.
Located only about 200 light-years from the Solar System, its extensive atmosphere makes it a prime target for analyzing its composition by measuring the spectrum through the transmission of light from its star as it passes through its atmosphere (see video above for details). Almost six years ago, astrophysicists discovered the presence of helium helium through observations with Hubble in the infrared.
All of these observations represent tests and constraints on the chemical and dynamic models of WASP-107b. For example, we did not initially expect to find sulfur dioxide. But new models of photochemical reactions now explain his discovery.
On the other hand, the lack of detection of methane is still unclear, which leads us to question the previously known models of exoplanet atmospheres!
We also know that the signal for water vapor and sulfur dioxide is weak enough to suggest that clouds are blocking some of this signal. These clouds must consist precisely of small silicate particles. Although clouds have been discovered on other exoplanets, this is the first time that astronomers have been able to clearly determine the chemical composition of these clouds.
Chemistry influenced by atmospheric dynamics
The KU Leuven press release accompanying a publication in the journal Nature said that researchers were surprised to find silicate clouds at high altitudes. In fact, the temperature there is only about 500 °C, which means that the silicate particles can form at higher temperatures due to the fusion temperature deeper in the atmosphere, and that the particles must even be raindrops of liquid, liquid silicates. How then is it possible that these high altitude sand clouds exist and continue to exist?
The press release then contains the explanations of one of the main astrophysicists behind the discovery, Michiel Min: “The fact that we see these sand clouds high in the atmosphere must mean that the sand rain droplets are evaporating in deeper and very hot layers and the resulting ones.” Silicate vapor is effectively drawn upwards, where it condenses again and forms silicate clouds again. This is very similar to the water vapor and cloud cycle on our Earth, but with droplets of sand. This continuous cycle of sublimation, sublimation, and condensation through vertical transport is responsible for the persistent presence of sand clouds in WASP-107b’s atmosphere. »
The press release concludes: “This groundbreaking research not only sheds light on the exotic world of WASP-107b, but also pushes the boundaries of our understanding of exoplanetary atmospheres.” It marks an important milestone in the study of exoplanetary planets and reveals the complex interaction of chemicals and climatic conditions on these distant worlds” and with the following comment from Achrène Dyrek, lead author of the discovery published in Nature, based in the Astrophysics Department of the CEA Paris: “JWST enables an in-depth atmospheric characterization of an exoplanet living in our solar system has no equivalent. We are discovering new worlds!” »
The researcher is one of the winners of the L’Oréal – UNESCO Young Talent Prize for Women and Science 2023 and a few months ago held a conference on the first results obtained with the JWST on the atmosphere of exoplanets. In the case of WASP-107b, Achrène Dyrek and her colleagues were able to carry out their work using the low-resolution spectroscope of JWST’s MiriMiri instrument, an infrared observation instrument in which the CEA played a key role.
A conference on February 4th, 2023 “First results from JWST: exoplanets in transit”, by Achrène Dyrek, Department of Astrophysics of the CEA. © French Physical Society
This work implies that the dynamics specific to an exoplanet’s atmosphere must be taken into account to predict and interpret the composition, which can be obtained from studying the transmission spectrum.