Exploring the ionosphere of Mars

The ionosphere of Mars is quite similar to Earth's ionosphere in some ways, but distinctly different in other ways. It possesses layers analogous to Earth's E and F1 layers, but is not immersed in a strong and global-scale dipolar magnetic field. I shall report recent results from studies of Mars Express measurements of vertical profiles of ionospheric electron density. On the dayside, these measurements show that the vertical structure of the ionosphere of Mars is more variable and more complex than previously thought, with the shape of the main peak and structure of the topside ionosphere changing dramatically and unpredictably. On the nightside, these measurements show that the ionosphere does not have a stable structure. The altitudes at which plasma layers are found varies between 80 and 160 km, and the peak plasma density varies by an order of magnitude at fixed solar zenith angle. Many of these observed phenomena have not been reproduced by theory, which indicates that much remains to be learned about this aspect of the Mars system. The ionosphere of Mars displays a much richer range of behaviors than suggested by numerical models, which suggests that the forthcoming MAVEN mission will make exciting discoveries concerning the ionosphere's chemistry, dynamics, and energetics.