The Three‐Dimensional Bow Shock of Mars as Observed by MAVEN

Abstract

The Martian magnetosphere is a product of the interaction of Mars with the interplanetary magnetic field and the supersonic solar wind. The location of the bow shock has been previously modeled as conic sections using data from spacecraft such as Phobos 2, Mars Global Surveyor, and Mars Express. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft arrived in orbit about Mars in November 2014 resulting in thousands of crossings to date. We identify over 1,000 bow shock crossings. We model the bow shock as a three-dimensional surface accommodating asymmetry caused by crustal magnetic fields. By separating MAVEN's bow shock encounters based on solar condition, we also investigate the variability of the surface. We find that the shock surface varies in shape and location in response to changes in the solar radiation, the solar wind Mach number, dynamic pressure of the solar wind, and the relative local time location of the strong crustal magnetic fields (i.e., whether they are on the dayside or on the nightside).Plain Language Summary A shock wave forms when the supersonic solar wind flows around objects in the Solar System. We studied the shape of this bow shock at Mars; the obstacle to the solar wind at Mars is the upper atmosphere and the patches of the crust that have localized strong magnetic fields. Previous studies have shown that the Martian bow shock can change due to changing solar wind or the location of crustal magnetic fields. Two-dimensional equations have been used to create mathematical models of the Martian bow shock, but they have implicit assumptions about the symmetry of the surface. Using over 2 years of observations from Mars Atmosphere and Volatile Evolution Mission, we have used a general surface equation to model the Martian bow shock fully in three-dimensions, which is able to represent the asymmetric shape of the surface. We find that while changes in the solar wind change the size of the Martian bow shock, the location of the crustal fields are most important factor in producing the asymmetric shape of the shock. Investigating how the bow shock varies under different solar wind conditions can be important toward understanding of how the Sun impacts the Martian magnetosphere that can drive important processes, such as atmospheric.

Importance of Ambipolar Electric Field in Driving Ion Loss From Mars: Results From a Multifluid MHD Model With the Electron Pressure Equation Included

“…This clearly demonstrates that the large north-south asymmetry of the bow shock locations in Case 1 is mainly caused by the presence of a strong crustal field in the southern hemisphere. This is also consistent with MAVEN results (Gruesbeck et al, 2018). Figure 4) shows a comparison of the ion and electron pressure (and temperature) distributions in the XZ plane using three different models for Case 1.…”

The Effects of Crustal Magnetic Fields and Solar EUV Flux on Ionopause Formation at Mars

“…This behavior is expected when one considers pressure balance across the interface. At Mars, similar trends are found in plasma boundaries such as the bow shock, MPB, ion composition boundary, and pressure balance boundary (Crider et al, ; Edberg et al, ; Gruesbeck et al, ; Halekas et al, ; Matsunaga et al, ; Ramstad et al, ; Vignes et al, ). However, as shown in Figure b, the flaring of the ionopause is much weaker, suggesting that pressure balance may not be the only mechanism that controls the formation of the ionopause at Mars.…”

Structure and Variability of the Martian Ion Composition Boundary Layer

“…Thanks to its comprehensive suite of plasma instrumentation, MAVEN provides the most complete set of measurements of the ICB since the Phobos‐2 mission, and its elliptical orbit and high time resolution (in particular, significantly higher cadence than previous ion measurements) provide frequent and precise measurements of the boundary location and structure. Several authors (Fang et al, ; Gruesbeck et al, ; Matsunaga et al, ) have already used the combined set of MAVEN measurements to locate and characterize boundaries, utilizing multiple data sets and a mix of automated and manual procedures to identify each individual boundary crossing. In this work, we develop algorithms to autonomously identify and characterize the structure of the ICB using a robust subset of the available measurements, enabling rapid automated analysis of a large number of observations, as also performed for a previous analysis of the bow shock (Halekas, Ruhunusiri, et al, ).…”

“…To accomplish this, we consider the distribution of ICB crossings, as shown in Figure . Rather than defining an asymmetric surface to represent the ICB (as done for the bow shock by Gruesbeck et al, ), we utilize a symmetric surface for computational simplicity and convenience. The exact functional form of this surface has no particular physical significance, and we use it only to determine the relative location of the ICB and to estimate its thickness.…”