Probing the Mars-Solar Wind Interaction With Numerical Modeling of High-Altitude Photoelectrons

The Electron Spectrometer (ELS) instrument of the ASPERA-3 package on the Mars Express satellite has observed photoelectron energy spectra up to apoapsis, and studies have indicated that their presence is due to direct magnetic connection between the dayside ionosphere and the observation locations in the magnetospheric flanks. Two numerical models are used to analyze the characteristics of these high-altitude photoelectrons. The first is a global, multi-species MHD code that produces a 3-d representation of the magnetic field and bulk plasma values around Mars. It is used here to examine the magnetic connectivity between the high-altitude flanks and the dayside ionosphere, and to determine where photoelectrons should be observed under various solar wind conditions. The second model is a kinetic electron transport model that calculates the electron velocity space distribution at points along a magnetic field line of the non-uniform Martian field. It is used here to simulate the high-altitude electron velocity-space distribution for comparison with the ELS measurements. Systematic features in the electron distribution provide information about the Mars-solar wind interaction. The possibility of using photoelectrons as tracers of atmospheric escape is discussed.