A POSSIBLE TRACE CARBON DIOXIDE POLAR CAP ON IAPETUS

摘要

We model ballistic transport of CO_2 on the surface of Iapetus, accounting for gravitational binding energy and polar cold traps. We find that if CO_2 is in the form of ice, it has a long enough residence time to be spectroscopically detected. We determine that at midlatitudes, CO_2 is volatile, will rapidly ablate, and be sequestered in a polar cold trap. In addition, we find that due to the inclination of Iapetus's orbit, the poles provide only a temporary cold trap, requiring the CO_2 to move to the opposite pole at the end of the winter season. During each transit, 5% of the CO_2 will reach escape velocity and be lost from the system. Finally, we make a prediction of the latitudinal extent and thickness of a possible CO_2 polar cap that could be detected during Cassini's 2007 September flyby of Iapetus.