Changes in the Martian Magnetosphere due to the Radial Orientation of the Interplanetary Magnetic Field (IMF)

The radial orientation of the IMF in the solar wind is not very frequent, and offers an opportunity to investigate the changes it brings to the structure of the induced magnetosphere of Mars, which lacks an intrinsic global magnetic field. In this study, we present results from MAVEN observations made during times with a radial (sunward/anti-sunward) orientation of the Interplanetary Magnetic Field (IMF), and seek to identify the changes in the key features of the Martian magnetosphere during the radial IMF conditions. We look for the signatures of escaping heavy ions during the radial IMF configuration, to compare with the known processes of heavy-ion escape during times with more typical non-radial IMF orientations. We find that the motional electric field can still contribute to the escape of heavy ions, including O+ and O2+, during the radial orientation, since the motional electric field can still have a non-zero value even during times with a relatively small cone angle. The results also show that there is no well-defined bow-shock during radial IMF configurations, and that the bow shock is replaced by large instabilities which extend into the upstream solar-wind region. These instabilities in the upstream solar-wind region may be created by back-streaming ions.