On the existence of multiple CO icelines in circumplanetary disks

The formation of regular moons in the Solar System likely happened in circumplanetary disks (CPDs) around the young Jupiter and Saturn. To date, only two CPD candidates have been detected: one in the PDS 70 disk and another one in the AS 209 system. If exomoons form in CPDs, their composition will be regulated by the properties of the disk at the formation place. Particularly, the location with respect to the CO snowline is important because of its large molecular abundance.

The CO snowline appears where the dust equilibrium temperature in the midplane matches the CO desorption temperature. The major dust heating processes arise from planetary and stellar irradiation and commonly, the strength of the stellar radiation field is assumed to be constant throughout the CPD. In this work, I relaxed this assumption allowing dust attenuation to act. I hypothesize that a natural consequence of this relaxation is the existence of a second CO snowline at larger planetocentric distances.

To test this hypothesis, I developed a semi-analytical model for the radiative transfer including an attenuated stellar radiation field, where the level of attenuation is inversely proportional to the planetocentric distance. The resulting temperature profile shows an reversal point at intermediate planetocentric distances. The presence of this reversal point was verified using three-dimensional radiative transfer numerical simulations. I used the resulting temperarture profile to solve for the distance at which the equilibrium temperature equals the CO desorption temperature and found two roots mathematically valid. Physically, the second solution corresponds to a second snowline in the CPD.

What is the role of the second snowline for the radial drift of solids form the outer CPD? What are the implications of this for the formation of exomoons? Can we test this prediction observationally? This project is under development and will be the one of the chapters in my PhD thesis.