Electron-scale Current Layers in the Martian Magnetotail: Spatial Scaling and Properties of Embedding

Abstract

Current sheets (CSs) are widespread objects in space plasma capable of storing and, then, explosively releasing the accumulated magnetic energy. In planetary magnetotails the cross-tail CS plays an important role in the global dynamics of the tail and in the transformation of the magnetic energy into the kinetic and thermal energies of the ambient plasma. We have analyzed 114 crossings of the cross-tail CS by the MAVEN spacecraft at X MSO ∼ [−1.0, −2.8]R M. Magnetic field observations with high time resolution allowed the observation of the inner superthin CS (STCS) with a half-thickness L STCS ∼ (1–100)ρ e (ρ e is the gyroradius of thermal electrons) in 75 intervals of the CS crossings from our database. The STCS was embedded into a thicker ion-scale CS and provides 10%–50% of the total current density in the cross-tail CS. Our analysis has shown that the observed L STCS and the embedding parameter, σ emb, characterizing the contribution of the STCS to the total current density in the CS are well described by the novel analytical kinetic model of a multilayered CS with an inner embedded electron-scale layer: L STCS∼ (0.9–1.2)λ and σ emb ∼ (0.9–1.2) σ model, where the universal spatial scaling λ ∼ δ i 2/ρ P and the embedding parameter σ model ∼ δ i /ρ P are determined by the local ion inertial length (δ i ) and gyroradius of thermal protons (ρ P ) in the STCS.

Equilibrium Configurations of Super‐Thin Current Sheets in Space Plasma: Characteristic Scaling of Multilayer Structures

“…For strong anisotropy 𝐴𝐴 𝐴𝐴𝑎𝑎 = 1 (this is the marginal fire hose condition discussed by (Burkhart et al, 1992), we get the singular case 𝐴𝐴 𝐴𝐴𝑥𝑥 ( z𝑧) ∼ z𝑧1∕3 and current 𝐴𝐴 𝐴𝐴𝑦𝑦 for 𝐴𝐴 𝐴𝐴= 0 formally becomes infinite. There is nothing dramatic in it because this singularity is integrable and STCSs with such 𝐴𝐴 𝐴𝐴( z𝑧) profile were found earlier in the Martial magnetotail (Grigorenko et al, 2019(Grigorenko et al, , 2022Zelenyi et al, 2020) 42, although data on anisotropy were available only within the narrow range of parameters ( 𝐴𝐴 𝐴𝐴𝑎𝑎 ≤ 0.2 ). Correspondingly, all STCSs in our analysis have the usual linear 𝐴𝐴 𝐴𝐴( z𝑧) ∼ z𝑧 profile as was predicted by our theory.…”

“…For strong anisotropy $${\beta }_{a}=1$$ (this is the marginal fire hose condition discussed by (Burkhart et al., 1992), we get the singular case $${B}_{x}\left(\tilde{z}\right)\sim {\tilde{z}}^{1/3}$$ and current $${j}_{y}$$ for $$z=0$$ formally becomes infinite. There is nothing dramatic in it because this singularity is integrable and STCSs with such $$B\left(\tilde{z}\right)$$ profile were found earlier in the Martial magnetotail (Grigorenko et al., 2019, 2022; Zelenyi et al., 2020) but in more general case $${\beta }_{a}< 1$$ this singularity disappears and $${L}_{e}\sim 1-{\beta }_{a}$$ linearly grows with the decrease in $${\beta }_{a}$$. Magnetic field for these cases has already the usual linear magnetic profile: $${B}_{x}\left(\tilde{z}\right)\sim \frac{\tilde{z}}{1-{\beta }_{a}}$$.…”

“…The theory of CSs supported by quasi‐adiabatic ions developed in the beginning of 2000 years allowed to explain the general properties of TCSs observed by the multi‐point Cluster space mission: (a) the property of embedding (Runov et al., 2003), (b) single‐, double‐ and triple‐maxima of current density (Nakamura, 2006), (c) metastability of TCS configuration (Zelenyi et al., 2011). Observational data and numerical modeling suggested that the STCS embedded into a thicker ion‐scale TCS can provide rather large but not the dominant (from 10% to 30%) of the net current density in the cross‐tail CS (Grigorenko et al., 2022; Zelenyi et al., 2004b, 2006).…”

Magnetic Reconnection in the Martian Magnetotail: Occurrence Rate and Impact on Ion Loss

“…Since charged particles have a physical scale of gyration or diffusion in the electromagnetic field, the dynamic evolution of the CS strongly depends on its spatial scale. Observational events suggested that the thickness of the Martian magnetotail CS is comparable to, and sometimes even less than, the proton scale (Grigorenko et al., 2019, 2022; Harada et al., 2015, 2020). Theoretically, when the CS becomes thinner than the proton inertial length, multiple X‐line magnetic reconnection can be triggered (Fujimoto, 2006; Huang et al., 2011; Paschmann et al., 2013).…”

“…scale (Grigorenko et al, 2019(Grigorenko et al, , 2022Harada et al, 2015Harada et al, , 2020. Theoretically, when the CS becomes thinner than the proton inertial length, multiple X-line magnetic reconnection can be triggered (Fujimoto, 2006;Huang et al, 2011;Paschmann et al, 2013).…”