Atmospheric origin of cold ion escape from Mars

Cold ionospheric ions dominate the plasma escape from Mars. The flow pattern versus altitude, latitude and local time suggests a fairly symmetric transport of ionospheric plasma from the dayside into the nightside/tail region of Mars. An interesting aspect of the plasma escape from Mars is the large abundance of molecular ions, implying that the outflow source region extends down to the lower ionosphere where molecular ions dominate. We also find a fair amount of ionized molecular hydrogen, H-2(+), in the ion outflow, the H-2(+) outflow corresponding to some 1/10 of the H+ outflow. Because the cold ionospheric ion outflow is dominated by H+, H-2(+), O+ and O-2(+), the average CO2+ outflow corresponding to about 10% of the heavy ion outflow, we have made a stoichiometric analysis of the ion escape. Adding the total outflow of hydrogen and oxygen respectively, we get H/O = 0.6 - 1.3. Altogether this suggests that the ultimate origin of the bulk ion escape from Mars is a minor constituent in the Martian atmosphere - water. Citation: Lundin, R., S. Barabash, M. Holmstrom, H. Nilsson, M. Yamauchi, E. M. Dubinin, and M. Fraenz (2009), Atmospheric origin of cold ion escape from Mars, Geophys. Res. Lett., 36, L17202, doi: 10.1029/2009GL039341.