Statistical Study of Heavy Ion Outflows From Mars Observed in the Martian‐Induced Magnetotail by MAVEN

Abstract

It is important to include the effects of cold ions when we consider heavy ion outflows from Mars. We here report on statistical properties of heavy ion outflows (including cold ion outflows) observed by Mars Atmosphere and Volatile EvolutioN in the optical wake region. Using data from July 2015 to December 2017, we statistically investigate the effects of solar wind convection electric fields and crustal magnetic fields on the heavy ion outflows. Results show that the average density ratio of O+:O2+:CO2+ is ~29:68:04. In the southern hemisphere where the strong crustal magnetic fields are located, the heavy ion outflow flux becomes smaller and the relative contribution of molecular ions to heavy ion outflows is larger than the northern hemisphere. The solar wind convection electric field strongly affects the heavy ion outflows. Heavy ion density is larger in the −E (electric field) hemisphere than in the +E hemisphere, while the dependence of velocity is opposite. Acceleration by the solar wind convection electric field in the +E hemisphere is expected to cause these dependencies. The heavy ion flux is larger in the −E (total O: 8.6 × 106 cm–2/s) than in the +E hemisphere (2.9 × 106 cm–2/s) due to the large density in the −E hemisphere. Velocity ratios of O+ to O2+ suggest that heavy ion outflows with large velocities tend to have the same energy to each other, while the O+ to O2+ ions are more likely to have the same velocity in outflows with small velocities.

Phobos Surface Sputtering as Inferred From MAVEN Ion Observations

“…Relatively large fluxes of low energy protons, alpha particles, atomic oxygen, and molecular oxygen ions appear at energies of around 4 to 7 eV in the magnetotail. These cold ions are discussed in detail by Inui et al (2019) and are likely to have energies lower than what is shown here, as we do not correct for acceleration by the spacecraft negative surface potential. However, only ions with kinetic energies higher than 80 eV significantly sputter the surface of Phobos (see section 4), so that the spacecraft negative surface potential does not impact the conclusions of this study.…”

“…Ions that can impact Phobos have been observed in situ by three instruments onboard the 3‐month long Phobos‐2 mission (Barabash et al, ; Dubinin et al, ; Verigin et al, ), during more than 14 years by the ion instrument of the ASPERA‐3 experiment onboard Mars Express (Ramstad et al, , and references therein), and have now been sampled for more than 4 years by three ion instruments onboard the Mars Atmosphere and Volatile Evolution (MAVEN) mission (Halekas et al, ; Inui et al, ; Jakosky et al, ; Lee et al, ).…”

“…Phobos‐2, Mars Express, and MAVEN have shown that planetary ions at the orbit of Phobos are mainly protons, O + ions, O 2 + ions, and in a lower extent, CO 2 + ions. These ions come from two sources, the first one being directly the Martian ionosphere, as ions escape through the polar plume and Martian plasma wake (Dong et al, ; Dong et al, ; Dubinin et al, ; Inui et al, ; Verigin et al, ). Neutral particles from the Martian exosphere or neutral corona, which is large enough to extend upstream of the Martian bow shock, are the second seed population for planetary ions, created when neutral particles are ionized and then picked up and accelerated by the background electromagnetic environment, reaching energies higher than several tens of keV (Barabash et al, ; Rahmati et al, , , ).…”

Impact of Martian Crustal Magnetic Field on the Ion Escape

“…Observations by Dubinin, Modolo, et al (2019) and Inui et al (2019) have shown that an asymmetry of escape fluxes between both hemispheres may also be related with the sign of the B y component of the IMF. This effect is related to features of the induced magnetosphere-the ionospheric plasma at the nightside is pushed in the direction opposite to the direction of the motional electric field in the solar wind.…”

The Induced Magnetosphere of Mars: Asymmetrical Topology of the Magnetic Field Lines

“…We investigate how the asymmetry that is related with the motional electric field propagates to the tail. Note that different features of asymmetry of the Martian magnetosphere were discussed in Inui et al (2019), Dong et al (2015), Dubinin et al (2011), Chai et al (2019, Harada et al (2015), and Modolo et al (2016). Focus of this paper is close integration of the Mars Atmosphere and Volatile EvolutioN (MAVEN) observations, hybrid simulations, and physical interpretation.…”