Silicate clouds and a circumplanetary disk in the YSES-1 exoplanet system.

Young exoplanets provide an important link between understanding planet formation and atmospheric evolution1. Direct imaging spectroscopy allows us to infer the properties of young, wide-orbit, giant planets with high signal-to-noise ratio. This allows us to compare this young population with exoplanets characterized by transmission spectroscopy, which has indirectly revealed the presence of clouds2-4, photochemistry5 and a diversity of atmospheric compositions6,7. Direct detections have also been made for brown dwarfs8,9, but direct studies of young giant planets in the mid-infrared were not possible before James Webb Space Telescope10. With two exoplanets around a solar-type star, the YSES-1 system is an ideal laboratory for studying this early phase of exoplanet evolution. Here we report the direct observations of silicate clouds in the atmosphere of the exoplanet YSES-1 c through its 9-11 µm absorption feature, and the first circumplanetary disk silicate emission around its sibling planet, YSES-1 b. The clouds of YSES-1 c are composed of either amorphous iron-enriched pyroxene or a combination of amorphous MgSiO3 and Mg2SiO4, with particle sizes of ≤0.1 μm at 1 millibar pressure. We attribute the emission from the disk around YSES-1 b to be from submicron olivine dust grains, which may have formed through collisions of planet-forming bodies in the disk.