Ion Composition Boundary Layer Instabilities at Mars

Abstract

The ion composition boundary layer that separates solar wind from ionospheric plasma at Mars typically contains a smooth compositional transition. However, ~10% of boundary crossings display large nonmonotonic variations in density, indicating an instability. We find that most of these instabilities occur on the flanks or downstream of the planet, and many fall into two distinct classes, which occur in different locations, under different preferred conditions. Plume events, which occur where the solar wind electric field points outward, likely represent the motion of the escaping ion plume across the spacecraft. Snowplow events, which occur where the electric field points inward, likely represent the escape of discrete parcels of plasma, which could account for ~10% of the total ion loss from Mars. Snowplow events occur under conditions that favor the development of ionospheric irregularities, which could form a seed for the snowplow mechanism that detaches and accelerates ionospheric plasma downstream.

A Comparative Study of Magnetic Flux Ropes in the Nightside Induced Magnetosphere of Mars and Venus

“…Therefore, Mars possesses a hybrid magnetotail and could give rise to various mechanisms to form flux ropes, including detachment of Martian crustal field (Brain et al., 2010), reconnection between the draped IMF (e.g., Eastwood et al., 2012), reconnection between crustal field and draped IMF (e.g., Hara, Seki, Hasegawa, Brain, Matsunaga, Saito, & Shiota, 2014; Vignes et al., 2004; Hara, Brain, et al., 2017; Krymskii et al., 2002) and ionospheric plasma instabilities in the draped IMF subsequently transported from the dayside (e.g., Elphic & Russell, 1983a; Hara, Harada, et al., 2017). Moreover, detached flux ropes (as well as plasma clouds) filled with a large amount of ionospheric plasma can potentially cause significant ionic escape from Mars (e.g., Brain et al., 2010; Halekas et al., 2016; Halekas et al., 2019).…”

MAVEN Observations of the Kelvin‐Helmholtz Instability Developing at the Ionopause of Mars

“…Note that the quasi-perpendicular magnetic fields in the transition region are draped interplanetary magnetic fields moving downwards as illustrated in Figure 4a. The K-H vortices can be accelerated by the magnetic tension, indicating that the snowplow effect (Halekas et al, 2016(Halekas et al, , 2019 has an impact on the K-H vortices. As suggested by Halekas et al (2016), the K-H instability can produce initial plasma bubbles to form snowplow structures.…”

“…This event has been identified as a snowplow event by Halekas et al. (2019). However, besides the snowplow effect, the K‐H instability can be verified and is required to interpret the observations.…”

Observations of Energized Electrons in the Martian Magnetosheath

“…The transition from the sheath to the planetary plasma occurs over a region identifiable by multiple observational signatures. In this transition region, one can find for example the "magnetic pileup boundary" or "MPB" (Acuna et al, 1998), Ion Composition Boundary (e.g., Halekas et al (2019)), and Induced Magnetospheric Boundary (Lundin et al, 2004). The exact location of the boundary is not crucial for the outcome of this paper, so we will adopt the empirical position of the MPB reported in Vignes et al (2000) to locate this transition region.…”