Aggregate Aerosols in the Virga Cloud Code: First Model Results

We introduce new functionality to treat fractal aggregate aerosol particles for planetary, exoplanetary, and substellar atmospheres within the Virga cloud modeling framework. Previously, the open source cloud modeling code Virga assumed spherical particles to compute particle mass and size distributions throughout the atmosphere. The initial release of Virga also assumed spherical particles to compute Mie scattering properties. However, extensive evidence from solar system aerosols, astrophysical disks and dust, and Earth climate studies suggests that aggregate particles are common compared to idealized compact spherical particles. Following recent advances in microphysical and opacity modeling, we implement a simple parametrization for dynamical and optical effects of fractal aggregate particles into Virga. We then use this new functionality to perform case studies of canonical cloudy exoplanets. We compare previous fractal aggregate particle treatments to our methods and show how our new fractal treatment affects theoretical spectra of cloudy atmospheres, which has important implications for observations from Hubble, JWST, and eventually Roman and Ariel. Overall, our model is faster and more flexible for a wider range of parameter space than previous studies. We explore the limitations of our modeling set-up and offer guidance for future investigations using our framework.