The Impact of Radial Interplanetary Magnetic Field (IMF) Events on the Solar Wind-Magnetosphere Interaction at Mars

The Interplanetary Magnetic Field (IMF) is carried radially outward into our Solar System by the solar wind and can play an important role in driving the large- and small-scale structure of a planet’s magnetosphere. This structure in turn determines whether or not, and how efficiently, the solar wind flow is deflected about the planet. Mars, as an unmagnetized body, has an induced magnetosphere due to its interaction with the solar wind, making it particularly susceptible to IMF driving. During “normal” solar conditions the IMF is in the Parker Spiral orientation, which reaches Mars with magnetic field lines roughly perpendicular to the planet’s dayside magnetosphere. This results in a “standard draping” of magnetic field lines about the planetary obstacle, leading to efficient deflection of the solar wind flow around Mars via the formation of several plasma boundaries and regions that include the planet’s bow shock and magnetosheath. These conditions are equivalent to quasi-perpendicular shock conditions upstream of the planet. However, it is known that “radial IMF” conditions can occur at Mars, whereby the IMF is aligned (almost) parallel along the Sun-Mars line, equivalent to quasi-parallel bow shock conditions upstream of the planet. Qualitatively, we anticipate that the Mars-solar wind interaction (both the key physical processes and resulting magnetospheric structure) can change substantially under such conditions, but the details have not been investigated in detail.

We present a case study of varying IMF orientations at Mars, specifically 2 radial IMF cases and one perpendicular IMF case, in which we focus on the resulting morphology and dynamics of the magnetosphere. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission acquires magnetic field data with its magnetometer instrument with which we can calculate the IMF orientation when the spacecraft samples the pristine solar wind. By studying events when MAVEN traverses the pristine solar wind and magnetosphere, the impacts upon the Martian plasma environment become clear. Our preliminary results suggest that during radial IMF conditions there are drastic changes in the interaction between the solar wind and the Mars magnetosphere, as well as the structure of the induced magnetosphere. Recent studies have supported this, showing that the induced magnetosphere can degenerate in times of radial IMF through analysis of spacecraft data and hybrid simulations (Zhang et al., 2024). Preliminary results in our study show that this degenerative magnetosphere does not deflect the solar wind around the planet as efficiently as when there are roughly perpendicular IMF conditions. This is essential to study, as this directly allows solar wind particles to penetrate into the ionosphere, where they deposit additional energy and may aid phenomena, such as atmospheric escape. This study will discuss the resulting magnetospheric structure and dynamics, as well as analyze the differences in solar wind deflection with varying IMF orientation.