Comparison of Global Martian Plasma Models in the Context of MAVEN Observations

Abstract

Global models of the interaction of the solar wind with the Martian upper atmosphere have proved to be valuable tools for investigating both the escape to space of the Martian atmosphere and the physical processes controlling this complex interaction. The many models currently in use employ different physical assumptions, but it can be difficult to directly compare the effectiveness of the models since they are rarely run for the same input conditions. Here we present the results of a model comparison activity, where five global models (single-fluid MHD, multifluid MHD, multifluid electron pressure MHD, and two hybrid models) were run for identical conditions corresponding to a single orbit of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We find that low-altitude ion densities are very similar across all models and are comparable to MAVEN ion density measurements from periapsis. Plasma boundaries appear generally symmetric in all models and vary only slightly in extent. Despite these similarities there are clear morphological differences in ion behavior in other regions such as the tail and southern hemisphere. These differences are observable in ion escape loss maps and are necessary to understand in order to accurately use models in aiding our understanding of the Martian plasma environment.

Structure and Variability of the Martian Ion Composition Boundary Layer

“…Boesswetter et al () and Simon et al () made similar arguments regarding the asymmetry of the ICB, and showed hybrid simulation results consistent with these expectations. Other Mars plasma simulations with appropriate physics included (for instance, hybrid and multifluid MHD models) typically display similar features (Brecht & Ledvina, ; Dong et al, ; Modolo et al, , ; Najib et al, ), albeit with differences in the details, as expected given the differences in implementation of the various models (Brain et al, ; Egan et al, ). One of our primary purposes in this study is to determine whether MAVEN observations can confirm or disprove these expected asymmetries.…”

Stellar influence on heavy ion escape from unmagnetized exoplanets

“…Here we describe some of the general differences and motivate our selection of parameters. Our initial base case (R0), is the same as that studied by Egan et al (2018), and is an example of a typical solar wind experienced by Mars. The final case (R4), is identical to the case considered for Trappist-g by Dong et al (2018), where the stellar wind was reconstructed using the Alfven Wave Solar Model (van der Holst et al 2014).…”

Ion Composition Boundary Layer Instabilities at Mars

“…Instead, the spatial location of the plume may vary with time, in response to either variations in upstream parameters or local dynamics. Most simulations predict that the plume has a relatively narrow structure (Egan et al, ). If a narrow dense plume moved back and forth across the orbit plane (i.e., a “flapping” motion), it could lead to signatures like those observed.…”