In September 2007 the Cassini spacecraft flew by Iapetus while the moon was in the solar wind, upstream of Saturn. The spacecraft approached from downstream and to the side, but did not pass through the moon's geometric wake. As Cassini reached a point where the interplanetary magnetic field would have connected the spacecraft to Iapetus, the magnetometer observed a strong, and unexpected, perturbation about the diameter of the moon in size. When mapped towards the moon, the perturbation rotates the magnetic field to avoid Iapetus. This perturbation was unlike other variations in the solar wind. Using a three-dimensional simulation of the solar wind-Iapetus interaction, we find that Cassini was too far from the moon to observe the signature due to an inert body. Two familiar sources of perturbations near planetary bodies are mass loading (ionization of neutral gas) and magnetization. Recent work has postulated that Iapetus loses material from the surface via sublimation, but no direct observations of this process have been made. The Earth’s Moon and Mars have crustal magnetization, but Jupiter’s Ganymede is the only non-planetary body confirmed to have a global magnetic field strong enough to deflect the surrounding plasma flow. We use the observations and results from simulation to explore the possibility of and place limits on any mass loading or magnetization at Iapetus.

Recent work has postulated that Iapetus loses material from the surface via sublimation