Current Systems at Moons

Abstract:

We review the modeling and modeling results for current systems at differnt moons. We focus on the Moon, but also discuss other moons in the solar system, e.g., Rhea and Callisto. Currents can be present

• in the interior,
• in the ionosphere, or
• in the surrounding plasma.

The importance of the currents in these different regions will be different for different objects. For the Moon, the currents in the interior and in the surrounding plasma are most important since the ionosphere is so tenuous. For other moons like Callisto, all three current systems are important.
The modeling of current systems present some numerical challenges. 
For particle models the magnetic fields are often noisy. Since currents are computed by derivatives of the magnetic fields, the computed currents will not be smooth. 
We also discuss advantages and disadvantages of computational methods that use currents instead of magnetic fields as primary variables. 
The modeling of interior currents implies that a magnetic diffusion equation has to be solved. In the algorithm this region has to be coupled to the external plasma region. This can also introduce a large range of timescales. 
For moons without a significant ionosphere there is also the numerical challenge of how to handle the low density regions in the wake of the moon.