Multi-spacecraft studies of plasma boundaries at Mars

We study the solar wind interaction with Mars and the location, shape, dynamics and controlling factors of the magnetic pileup boundary (MPB) and the bow shock (BS), which form as a result of this interaction, by using single as well as two-spacecraft measurements. By using Mars Global Surveyor (MGS) measurements we produce statistical models of the shapes of the two boundaries. The influence on the boundaries from the crustal magnetic fields of Mars is also studied. We find that the MPB is pushed to higher altitudes depending on the strength of the underlying crustal fields while the BS is found at higher altitudes over the entire southern hemisphere of Mars, where the crustal fields are strongest. By using the simultaneous measurements from Rosetta and Mars Express (MEX) we study the boundaries during high and low solar wind dynamic pressure. During low pressure, simultaneous two-spacecraft measurements provide leverage on the accuracy of the shape of the MPB and BS. Their previously modelled shapes are found to be in agreement with the shapes derived from these two-point measurements. During high pressure, we observe how the boundaries become asymmetric in their shapes, possibly due to increased plasma outflow over one hemisphere, which lowers the plasma pressure on that side of the planet and results in an asymmetric shape. By using MGS and MEX measurements we study the altitude of the boundaries as functions of solar wind dynamic pressure, solar EUV flux and crustal magnetic field strength. We also examine the effect of the direction of the interplanetary magnetic field on the boundaries. We find that the dynamic pressure, EUV flux and crustal magnetic fields are the main governing factors of both the MPB and the BS.