Statistical Properties Of Solar Wind Upstream Of Mars: Maven Observations

Using the data sets of Mars Atmosphere and Volatile EvolutioN and OMNI for the period 2014 October 10-2020 February 14 and the heliocentric distance of 1-1.66 au, we investigate the statistical properties of solar wind upstream of Mars for the first time. The key parameters, including interplanetary magnetic field (IMF), proton density (N), bulk velocity ( divide V divide ), and dynamic pressure (P (dyn)), are surveyed with regard to variations of solar activity level and heliocentric distance. We find that the parameters divide IMF divide , N, and P (dyn) monotonously decrease with heliocentric distance. Both divide IMF divide and P (dyn) are generally stronger at a higher solar activity level (F (10.7) >= 70 sfu), while such activity has little relevance to N. In contrast, divide V divide basically keeps a median of about 370 km s(-1) and is insensitive to the solar activity level and heliocentric distance. We also find that the IMF upstream of Mars at the higher solar activity level has a much smaller spiral angle in the inward sector; thus, IMF seems "straighter" than that in the outward sector, although that is not so for the inward sector of the upstream of Earth. Our statistical survey can be used as a reference for upstream solar wind of Mars at 1.4 similar to 1.7 au, and could benefit the studies on solar wind as well as the Martian space environment.