A COMPUTATIONAL MODEL FOR ICE MIGRATION ON THE SURFACES OF AIRLESS BODIES

All icy moons in the Jovian and Saturnian systems are - with the exception of Titan - airless bodies. The long-range migration of volatiles from and onto these surfaces therefore is not dominated by exchange of volatiles with an atmosphere and solar radiation is directly absorbed (or reflected) by the surfaces. A physical model of the processes of absorption, sublimation and deposition therefore is comparatively straightforward. Our computer model can simulate the migration of volatiles under these circumstances.

The model tessellates the surfaces of an airless body into triangles of equal size. Each triangle has different surface properties that evolve while the model simulates a long-term development. A rate network of net migration is calculated from sublimation and redeposition under the assumptions of

1. a slowly rotating body,

2. undisturbed ballistic molecular trajectories,

3. isotropic emission,

4. Maxwellian speed distributionm and

5. high sticking coefficients of the surfaces.

The model was originally developed for conducting research on the global black-and-white dichotomy of the Saturnian moon Iapetus and was able to reproduce the anomaly qualitatively. Comparing our results to those of [Spencer and Denk, 2010] proposing a positive thermal feedback process results in a time-scale of the same order of magnitude with a tendency towards slightly faster darkening compared to the `Model B´ referenced therein.