Dust Rains on Exoplanets: JWST Detects Silicate Clouds and Circumplanetary Disks

A new study based on observations of two exoplanets, conducted using the James Webb Space Telescope (JWST), has produced significant results, published in the prestigious journal Nature .

The planets in question orbit the star YSES-1, a young sun with an age of just 16.7 million years, located about 300 light years from our Solar System. By directly observing the light of these exoplanets, an international research team led by astrophysicist Kielan Hoch of the Space Telescope Science Institute in Baltimore, United States, has made extraordinary discoveries . The atmosphere of one of the two planets, YSES-1 c, has been observed to contain silicate clouds, composed of minerals that give it a reddish color. The other planet in the system, YSES-1 b, instead appears to be surrounded by a circumplanetary disk, also formed by silicates, from which smaller bodies, such as moons, could take shape in the future . Valentina D'Orazi, a researcher at the National Institute for Astrophysics (INAF) and the University of Rome Tor Vergata, also participated in the discovery.

The discovery, presented at the 246th meeting of the American Astronomical Society in Anchorage, Alaska, offers new insights into the early stages of formation of planetary systems similar to our own , giving researchers the opportunity to study in near-real time how a Jupiter-like planet is born and evolves.

" Observing silicate clouds, which are essentially sand clouds, in the atmospheres of extrasolar planets is important because it helps us better understand how atmospheric processes work and how planets form, a topic still under discussion since there is no agreement on the different models ," explains co-author Valentina D'Orazi, a researcher at the National Institute for Astrophysics (INAF) and the University of Rome Tor Vergata, currently a visiting research scholar at the University of Texas at Austin as part of the Fulbright program . " The discovery of these sand clouds, which remain aloft thanks to a cycle of sublimation and condensation similar to that of water on Earth, reveals complex mechanisms of transport and formation in the atmosphere. This allows us to improve our models of climate and chemical processes in environments very different from those of the Solar System, thus expanding our knowledge of these systems ."

The two planets in question are gas giants: YSES-1 c has a mass equal to 14 times that of Jupiter, while YSES-1 b has 6. Both are located at considerable distances from their star, about 5 and 10 times greater than the distance between the Sun and Neptune. It is precisely this very extended orbit that allowed the team to observe the two planets with the JWST through the technique of direct imaging, the application of which is still limited to a small number of planets with very particular characteristics. The study demonstrates the ability of the powerful space telescope to provide high-quality spectral data for exoplanets observed with this technique, opening new avenues for the study of atmospheres and circumstellar environments.

The presence of silicate clouds in exoplanet atmospheres has been predicted theoretically and indirectly deduced from previous observations. However, this research provides the first direct and spectroscopic observation of silicate clouds in a specific exoplanet, YSES-1 c . This provides insight into the atmospheric composition of a young gas giant, confirming the presence of high-altitude silicate clouds, containing either iron-rich pyroxene or a combination of bridgmanite (MgSiO3) and forsterite (Mg2SiO4).

For the twin planet YSES-1 b, this work presents the first detection of silicate emission from a circumplanetary disk, a sort of "mini-Solar System" in formation . Only two similar circumplanetary disks had been observed previously, and the new research provides direct information on the composition and physical processes in these environments: the presence of submicron-sized olivine grains, in fact, suggests a formation mechanism through collisions of small bodies, called planetesimals, within the disk.

" By studying these planets we can better understand how planets form in general, a bit like peering into the past of our Solar System ," concludes D'Orazi . " The results support the idea that the composition of clouds in young exoplanets and circumplanetary disks play a crucial role in determining the atmospheric chemical composition. Furthermore, this study underscores the need for detailed atmospheric models to interpret the high-quality observational data obtained with telescopes such as JWST ."