Photoelectron Pitch Angle Distributions at Mars

Observations of electron pitch angle distributions (PADs) have suggested collisions are not the only pitch angle scattering process occurring in the Martian ionosphere [Liemohn et al., 2003]. High energy (>100eV) electrons were observed to be isotropized, indicating an energy dependent scattering process not previously studied on Mars. Pitch angle scattering has an effect on the number of precipitating electrons, which cause ionization and heating of the atmosphere, and can contribute to atmospheric escape. We define a pitch angle isotropy ratio as the average field aligned flux (0˚-45˚,135˚-180˚) divided by the average flux at perpendicular pitch angles (45˚-135˚) for a given energy. Using 2 years of MAVEN observations, we statistically analyze SWEA data in order to identify regimes of the Martian space environment where these isotropic high energy PADs occur most frequently. Preliminary results show that these PADs occur more frequently at electron densities less than 750 cm^-3, regardless of altitude. Whistler mode waves, which are an energy dependent pitch angle scattering process, are dependent on the electron density. Comparisons to idealized scenarios will be performed using a superthermal electron transport model.