Interplanetary Dust Ablation Seeds Silicate Clouds in Exoplanet Atmospheres

Abstract: Interplanetary dust particles (IDPs) are present throughout the Solar System, with Earth experiencing a mass flux of roughly 100 tonnes of IDPs per day. These particles ablate in the upper atmosphere, delivering aerosols that form noctilucent and stratospheric clouds. Since IDPs are present in exoplanet systems as exozodiacal dust disks (exozodis), it is likely that exoplanets experience a constant infall of IDPs as well. In this work, we investigate the effect of IDPs on the cloud structure of gas-giant exoplanets and brown dwarfs, and determine their observability. We apply the microphysical cloud model Nimbus to the Sonora Diamondback model grid to cover a wide range of effective temperatures, surface gravities, atmospheric mixing constants, and IDP mass fluxes. Our results show that IDP infall increases cloud particle number densities, decreases cloud particle radii, and enhances silicate features in transmission and thermal emission spectra. Exoplanets with lower atmospheric mixing rates, effective temperatures, and gravity are more sensitive to IDPs. Most notably, they lead to observable silicate absorption features in colder planets where silicate clouds would otherwise not be observable. WASP-107 b is an example of such an exoplanet with observational evidence of silicate particles. Using Nimbus, we found that a 100 times Earth-like IDP mass flux with a Solar-System-like IDP composition of quartz (SiO2), enstatite (MgSiO3), and iron (Fe) can explain the observations of high altitude silicate particles in WASP-107 b.