Slowly but surely, month by month, the James Webb Space Telescope is providing more and more evidence of its ability to provide details on structure. AtmosphereAtmosphere Extraterrestrials Of course, the ultimate goal is to find solid biosignatures in an extraterrestrial environment, but that will require us to be patient, perhaps for decades. This does not mean that such signings will not take place before 2030. It may take a very long time to be reasonably certain that there is no natural process inorganicinorganicNot associated with the existence of life, capable of generating observed signals.

One of the strategies to achieve this holy grail is to learn as much as possible about the atmospheres of exoplanets, even when it comes to uninhabited gas giants. hot jupiterhot jupiter Or Les Mini-Neptunes.

Therefore it is with a certain interest that we learn today the results achieved by a teamastronomersastronomers Co-directed by researchers from the European, CEA and the Institute of Astronomy of KU Leuven, the renowned Belgian University of Leuven. They worry about the comments of JWSTJWST Revealing the composition of the atmosphere of the exoplanet WASP-107b. The resulting spectrum shows the presence of not only water vapor molecules, but also sulfur dioxide, SO22, presence of cloudsclouds Silicate particles, cousins ​​of grains sablesable, was also established; However, no trace of methane (CH)4), and it’s amazing.

A planetary atmosphere has a spectral signature that represents its chemical composition, but clouds and “fog” also have a spectral signature that represents its composition. Thanks to several techniques, it is possible to determine the physicochemical characteristics of an exoplanet’s atmosphere. These techniques include: spectroscopic transits, secondary transits or eclipses, direct spectroscopic observations of the planet or even observations of the planet at different phases around the star to measure temporal and seasonal variations. Discover exoplanets through our 9-episode web series, available on our YouTube channel. A playlist proposed by CEA and the University of Paris-Saclay as part of H2020 Exoplanets—a European research project. © CEA

Absence of methane challenges planetary scientists

WASP-107b had already been observed with the Hubble telescope years ago. In fact, we have known for some time that it is one of the lowest density exoplanets known. In fact, although it is collectivelycollectively or only 12% of Jupiter’s diameter, its diameter is comparable because it is extremely hot by starstar Host (slightly cooler than us and less spacious). SoleilSoleil), around which it loops To revolve aroundTo revolve around In just six days. With temperatures reaching hundreds of degrees and above, the atmosphere expands to such an extent that researchers sometimes refer to WASP-107b as a “cotton candy” planet ( cotton candy In English).

Since it is located only around 200 light yearslight years Of Solar systemSolar system, its atmosphere is so diffuse, for this reason, it is a favorite target to analyze its composition by measuring the spectrum by the transmission of its star’s light after it has passed this atmosphere (see the video above for more details) . About six years ago, AstronomyAstronomy had already detected the presence ofheliumhelium by observing with HubbleHubble in L’infraredinfrared,

All of these observations test and constrain the chemical and dynamical models of WASP-107b. For example, we did not initially expect to find sulfur dioxide. But new models of photochemical reactions now explain its discovery.

On the other hand, the lack of detection of methane is unexplained, leading us to question the models of exoplanet atmospheres known so far!

We also know that the signal for water vapor and sulfur dioxide is so weak that it means clouds are blocking some of this signal. These clouds must be made of tiny silicate particles. Although clouds have been discovered before on other exoplanets, this is the first time that astronomers have been able to definitively identify the chemical composition of these clouds.

Chemistry affected by atmospheric dynamics

Press release of KU Leuven, accompanying a publication in the newspaper Nature, Explain that the researchers were surprised to see that these clouds silicatesilicate Are at altitude. Actually, the temperature there is only around 500°C. But considering the temperature FusionFusion Silicate particles They can form at higher temperatures, deeper in the atmosphere, so it is also expected that these particles will form silicate precipitation Liquid substanceLiquid substance, So how is it possible that these sand clouds exist and persist at such high altitudes?

The press release offers an explanation from Michael Min, one of the main astrophysicists behind the discovery: ” The fact that we see these sand clouds high in the atmosphere must mean that sand rain droplets are evaporating in deep, very hot layers and the resulting silicate vapor is effectively rising upward. where it condenses again to form silicate clouds. This is similar to the water vapor and cloud cycle on our own Earth, but with droplets made of sand. this continuous cycle sublimationsublimation and of evaporationevaporation Vertical transport is responsible for the permanent presence of sand clouds in WASP-107b’s atmosphere. ,

The press release ends by saying ” This pioneering research not only sheds light on the world ForeignerForeigner of WASP-107b, but also pushes the limits of our understanding of exoplanetary atmospheres. This is an important milestone in extraterrestrial exploration, highlighting the complex interplay of chemicals and climatic conditions on these distant worlds. » And published with the following comment from Akrene Dierek, the lead author of the discovery Natureposted in the departmentastrophysicsastrophysics du CEA Paris: « JWST allows deep atmospheric characterization of an exoplanet that has no counterpart in our Solar System, we are discovering new worlds! ,

A conference on April 2, 2023, “First results from JWST: Exoplanets in transit”, by Achareen Dirac of the CEA Astrophysics Department. © French Physical Society

The researcher is one of the winners of the L’Oréal – UNESCO Young Talent Award 2023 for Women and Science and, a few months ago, she gave a conference on the first results obtained with JWST regarding the atmospheres of exoplanets. In the case of WASP-107b, Acheren Dirac and his colleagues were able to do their job, thanks to spectroscopespectroscope base ResolutionResolution of the instrument MiriMiri JWST, an instrument observing in the infrared and to which CEA was a major contributor.

The implication of this work is that the specific dynamics of an exoplanet’s atmosphere must be taken into account in order to predict and interpret the structure that can be obtained from the study of the transmission spectrum.

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