Constraints on aerosol structure and formation in the atmosphere of the ice giants from microphysics simulations

A number of images and analyses have demonstrated the presence of hazes and clouds in the atmosphere of the ice giants. While the formation of hazes is attributed to the methane dissociation in the high stratosphere by solar UV and energetic particles that leads to a number of chemical reactions (e.g. Moses et al., Icarus, 307, 2018), the observed clouds are the result of the condensation of CH₄ and H₂S in the troposphere (e.g. Irwin et al., Nature Astronomy, 2018). However, the lack of current limb observations taken at different tangent heights limits our knowledge about the vertical structure and optical properties of these aerosols. In this work, we will present different results obtained with a coupled cloud-haze microphysical model (Toledo et at., Icarus, 333, 2019; Toledo et at., Icarus, 350, 2020) used to constrain the particle size, density, vertical structure and time scale of aerosols in the ice giants. Our simulations show, among other results, high precipitation rates at pressures greater than 0.5 bar and timescales ranging from years (for the haze) to a few hours (CH₄ clouds).