Plasma clouds and snowplows: Bulk plasma escape from Mars observed by MAVEN. Issue 4 (25th February 2016)

• Record Type: Journal Article
• Authors: Halekas, J. S.; Brain, D. A.; Ruhunusiri, S.; McFadden, J. P.; Mitchell, D. L.; Mazelle, C.; Connerney, J. E. P.; Harada, Y.; Hara, T.; Espley, J. R.; DiBraccio, G.A.; Jakosky, B. M.
• Is Part Of: Geophysical research letters. Volume 43:Issue 4(2016)
• Page Start: 1426
• Page End: 1434
• Publication Date: 2016-02-25
• Subjects: Mars -- MAVEN -- atmospheric escape; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL067752
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We present initial Mars Atmosphere and Volatile EvolutioN (MAVEN) observations and preliminary interpretation of bulk plasma loss from Mars. MAVEN particle and field measurements show that planetary heavy ions derived from the Martian atmosphere can escape in the form of discrete coherent structures or "clouds." The ions in these clouds are unmagnetized or weakly magnetized, have velocities well above the escape speed, and lie directly downstream from magnetic field amplifications, suggesting a "snowplow" effect. This postulated escape process, similar to that successfully used to explain the dynamics of active gas releases in the solar wind and terrestrial magnetosheath, relies on momentum transfer from the shocked solar wind protons to the planetary heavy ions, with the electrons and magnetic field acting as intermediaries. Fluxes of planetary ions on the order of 10 7 cm −2 s −1 can escape by this process, and if it operates regularly, it could contribute 10–20% of the current ion escape from Mars. Key Points: Ionospheric plasma can escape from Mars in coherent structures or clouds Momentum is transferred from the solar wind to heavy ions by magnetic fields A snowplow effect accelerates parcels of unmagnetized Martian plasma