Liemohn M.W., Ma Y., Frahm R.A., Fang X., Kozyra J.U., Nagy A.F., Winningham J.D., Sharber J.R., Barabash S., Lundin R.
Space Science Reviews
Summary: Atmospheric photoelectrons have been observed well above the ionosphere of Mars by the ASPERA-3 ELS instrument on Mars Express. To systematically interpret these observations, field lines from two global MHD simulations were analyzed for connectivity to the dayside ionosphere (allowing photoelectron escape). It is found that there is a hollow cylinder behind the planet from 1-2 R M away from the Mars-Sun line that has a high probability of containing magnetic field lines with connectivity to the dayside ionosphere. These results are in complete agreement with the ELS statistics. It is concluded that the high-altitude photoelectrons are the result of direct magnetic connectivity to the dayside at the moment of the measurement, and no extra trapping or bouncing mechanisms are needed to explain the data. © Springer Science+Business Media, Inc. 2007.