Two Types of Martian Magnetotail Current Sheets: MAVEN Observations of Ion Composition

• Published in: Geophysical research letters 2023-01, Vol.50 (2), p.n/a
• Main Authors: Li, X. Z., Rong, Z. J., Fraenz, M., Zhang, C., Klinger, L., Shi, Z., Gao, J. W., Dunlop, M. W., Wei, Y.
• Format: Article
• Language: English
• Subjects: Charged particles; Composition; current sheet; Current sheets; Density; Dynamic pressure; Evolution; Heavy ions; Hydrogen; Ion composition; Ion density; Ion density (concentration); ion escape; ion species; Ions; Magnetotail plasma; Magnetotails; Mars; Mars atmosphere; Mars missions; Martian magnetotail current sheet; Nitrogen dioxide; Planetary magnetotails; Plasma dynamics; Protons; Solar wind; Solar wind density; Solar wind protons; Spacecraft; Upstream
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL102630

Using measurements from the Mars Atmosphere and Volatile EvolutioN mission, we investigate the densities of H+ (nH+ ${n}_{{\mathrm{H}}^{+}}$), O+ (nO+ ${n}_{{\mathrm{O}}^{+}}$), and O2+ (no2+ ${n}_{{\mathrm{o}}_{2}^{+}}$), respectively, in the Martian magnetotail current sheet. We find that the current sheet when it is closer to the terminator than 0.75 Mars radii is mostly dominated by heavy ions ((nO++no2+ ${n}_{{\mathrm{O}}^{+}}+{n}_{{\mathrm{o}}_{2}^{+}}$)>2 nH+ ${n}_{{\mathrm{H}}^{+}}$), regardless of the variation of the upstream solar wind, but that it is sometimes dominated by H+ (nH+ ${n}_{{\mathrm{H}}^{+}}$ >2(nO++no2+ ${n}_{{\mathrm{O}}^{+}}+{n}_{{\mathrm{o}}_{2}^{+}}$)) at downstream distances exceeding 0.75 Mars radii. The occurrence rate of the dominant H+ weakly increases (and that of the heavy ions decreases) with solar wind density and dynamic pressure. Our results suggest that solar wind protons could enter the Martian tail and may become the dominant ion species in the current sheet, particularly when the solar wind density or dynamic pressure is high. Plain Language Summary The current sheet of the Martian magnetotail is a major channel for the escape of planetary ions. The ion composition in the current sheet is essential to our understanding of this escape, as well as the magnetotail plasma dynamics. Our current knowledge, however, is poor. Based on the measurements of the ion density of different species in the current sheet from the Mars Atmosphere and Volatile EvolutioN spacecraft, we report that the current sheets we have surveyed are dominated by either the heavy ions from the planet or H+ (mostly) from the solar wind. We find that the downstream distance and the variation of the upstream solar wind are the two key factors that account for which ion species dominates in the tail current sheet. Key Points Current sheets are mostly dominated by heavy ions but are sometimes dominated by H+ at the downstream distance exceeding 0.75 Mars radii The occurrence rate of current sheets with dominant H+ (heavy ions) weakly increases (decreases) with solar wind density and dynamic pressure Our results suggest that the dominant H+ in the current sheet could originate from solar wind