The Drivers of the Martian Bow Shock Location: A Statistical Analysis of Mars Atmosphere and Volatile EvolutioN and Mars Express Observations

Abstract

The Martian interaction with the solar wind leads to the formation of a bow shock upstream of the planet. The shock dynamics appear complex, due to the combined influence of external and internal drivers. The extreme ultraviolet fluxes and magnetosonic Mach number are known major drivers of the shock location, while the influence of other possible drivers is less constrained or unknown such as crustal magnetic fields, solar wind dynamic pressure, or the Interplanetary Magnetic Field (IMF) intensity, and orientation. In this study, we compare the influence of the main drivers of the Martian shock location, based on several methods and published datasets from Mars Express (MEX) and Mars Atmosphere Volatile EvolutioN (MAVEN) missions. We include here the influence of the crustal fields, extreme ultraviolet fluxes, solar wind dynamic pressure, as well as (for MAVEN, thanks to magnetic field measurements) magnetosonic Mach number and Interplanetary Magnetic Field parameters (intensity and orientation angles). The bias due to the cross‐correlations among the possible drivers is investigated with a partial correlations analysis. Several model selection methods (Akaike Information Criterion and Least Absolute Shrinkage Selection Operator regression) are also used to rank the relative importance of the physical parameters. We conclude that the major drivers of the shock location are extreme ultraviolet fluxes and magnetosonic Mach number, while crustal fields and solar wind dynamic pressure are secondary drivers at a similar level. The IMF orientation also plays a significant role, with larger distances for perpendicular shocks rather than parallel shocks.

Interplanetary Magnetic Field Effect on the Location of the Martian Bow Shock: MAVEN Observations

“…However, the IMF intensity effect was not mentioned. Recently, Garnier et al (2022) found that the Martian terminator altitude, R TD , is apparently and positively correlated with the IMF intensity using the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express (MEX) observations, which were also observed on Venus (Chai et al 2014). Theoretically, a stronger draping induced by an enhanced IMF can lead to the BS moving away from the planet (Bertucci et al 2011).…”

“…Besides the above factors, the influence of the IMF on the BS cannot be ignored (e.g., Vignes et al 2002;Garnier et al 2022). However, there were fewer studies involving the effect of IMF intensity on the location of the Martian BS, especially for the observations.…”

In Situ Observation of Solar-flare-induced Proton Cyclotron Waves Upstream from Mars

“…The changes might be partly due to the enhanced solar irradiance from the X8.2 flare. It should be mentioned that, the MAVEN orbit did not extend outside of the Martian BS during the surrounding orbits (5714, 5715, 5718, and 5719), mainly owing to the changes of the location and shape of the Martian BS caused by both external and internal drivers (Garnier et al 2022). The present study focuses on the observations upstream from the BS during orbits 5716 and 5717.…”

Magnetic Fields and Plasma Motions in a Hybrid Martian Magnetosphere

“…(2000) for the MB location, for better agreement with ASPERA‐3 observations in the noon sector (Dubinin et al., 2006). It is worth noting that the average locations of these boundaries vary under the influence of different drivers (e.g., Garnier et al., 2002), including also the season and the solar cycle with slightly different parameters for the conics for the different Martian years covered by MAVEN (Simon Wedlund et al., 2022 and references therein).…”