Proton pitch angle distributions in the Martian induced magnetosphere: A survey of Tianwen-1 Mars Ion and Neutral Particle Analyzer observations

The pitch angle distributions of ions and electrons can be affected by various processes; thus, they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas. From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter, we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field, and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions. Even though no symmetrical features were seen in the dataset, we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV. Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region. Although our results are more or less restricted by the adopted magnetic field, they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere.