Radial interplanetary fields at Comets and Mars

Objects in the solar system are embedded in the solar wind and how they interact with it depends on their atmosphere and magnetic fields. Bodies without a global magnetic field, like Mars and comets, develop an induced magnetosphere. This region is an ideal plasma laboratory consisting of different ion species and dust particles that can be explored by spacecraft. Understanding the environment is crucial for future human exploration and our understanding of the solar system.

One of the main parameters determining the shape of the interaction region is the direction of the interplanetary magnetic field (IMF). Most models assume a unified "standard" direction of the field, which often gives good results. However, the IMF is highly variable, and a large part of cases is not covered in literature.

Plasma observations at both Mars and comet 67P/Churyumov-Gerasimenko recently showed unusual wave and particle activity that was not covered by the standard models, and which were attributed to a radial IMF configuration. For these cases the environment can change completely, and ion escape and acceleration rates are dramatically different. This has consequences for planetary atmospheric models and cometary tail observations that are poorly understood.

This is a knowledge gap that should be filled before the upcoming mission Comet Interceptor will encounter a comet and take multi-point measurements in this environment for the first time.

The key to understanding the environment under these special conditions is to relate existing numerical and analytical models to the observations and build new models that better describe the non-standard cases.