Solar wind measurements by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission provide samples of the heliosphere at 1.38–1.67 AU, and of the upstream conditions that drive numerous processes in the near-Mars plasma environment. We reduce ion measurements from MAVEN’s Solar Wind Ion Analyzer (SWIA), using contextual magnetic field measurements, to 13 independent macroscopic plasma parameters by fitting a convolution of SWIA’s 3-dimensional response function and a superposition of phase-space bi-kappa distribution functions to each measured distribution using an iterative Poisson optimization scheme. This ensemble of parameters represents the solar wind H + core, H + beam, and He 2+ (alpha) populations, effectively separating each population’s contribution to any measured distribution. Sporadic plasma frequency measurements from MAVEN’s Langmuir Probe and Waves (LPW) instrument are used to calibrate the SWIA measurements such that ion charge densities match LPW-derived electron charge densities. The resulting dataset is effectively ground-truthed, largely corrected for instrumental particularities, and provides a rich timeline of solar wind properties at Mars, including composition, velocities, temperature anisotropies, differential drifts, and degree of thermalization.
Ramstad et al. (Tue,) studied this question.