Tianwen-1 MINPA observations in the solar wind

Abstract

The Mars Ion and Neutral Particle Analyzer (MINPA) is one of the three scientific instruments onboard the Tianwen-1 orbiter to investigate the Martian space environment. During Tianwen-1’s transfer orbit to Mars, the MINPA was switched on to measure the solar wind ions. Here, we present the first results of the MINPA observations in the solar wind. During cruise, nearly half of the MINPA ion field-of-view (FOV) was blocked by the lander capsule; thus only the solar-wind ions with azimuthal speeds pointing towards the unblocked FOV sectors could be detected. We perform a detailed comparison of the MINPA’s solar wind observations with data from Earth-based missions when MINPA reached its count-rate peak, finding a general consistency of the ion moments between them. The blocking effect due to the lander is evaluated quantitatively under varying solar-wind velocity conditions. Despite the blocking effect, the MINPA’s solar wind measurements during the transfer orbit suggest a good performance.