Estimation of the spatial structure of a detached magnetic flux rope at Mars based on simultaneous MAVEN plasma and magnetic field observations

Abstract

Simultaneous Mars Atmosphere and Volatile EvolutioN mission (MAVEN) plasma and magnetic field observations reveal a detached magnetic flux rope in the Martian induced magnetosphere. The flux rope was identified by an increase in the magnetic field amplitude accompanied by smooth vector rotations. In addition, MAVEN observed a pronounced ion composition change across the structure, with solar wind ions dominating outside and planetary ions dominating within. Grad‐Shafranov reconstruction is applied to determine the two‐dimensional spatial structure of the flux rope. The event occurred near the dusk terminator, downstream from strong crustal magnetic fields. One possibility is that the flux rope was created by magnetic reconnection associated with interplanetary and/or crustal magnetic fields. A weak interplanetary coronal mass ejection (ICME) arrived at Mars a few hours before the event. A pressure pulse and turbulent magnetic fields due to the ICME might be responsible for driving magnetic reconnection to detach the flux rope from the crustal source.

MAVEN observations of a giant ionospheric flux rope near Mars resulting from interaction between the crustal and interplanetary draped magnetic fields

“…The plasma β ; the ratio of the plasma pressure relative to the magnetic pressure, can be computed to be approximately 0.3 across the structure. This feature is consistent with previous flux rope events detected by MAVEN [ Hara et al , , ].…”

“…Previous studies extensively described how to apply the GSR technique to the magnetohydrostatic structures in space [e.g., Hau and Sonnerup , ; Hu and Sonnerup , ; Hasegawa et al , ]. Hara et al [] explained optimal treatments to apply the GSR technique to the Martian flux rope, because MAVEN detected multiple ion species.…”

“…Hence, the spacecraft velocity could be the most dominant component to determine the motion of the observed ionospheric flux rope. Except for the above considerations, we apply the same GSR scheme described in Hara et al [] to the observed ionospheric flux rope. It should be mentioned beforehand that these STATIC low‐energy ion data calibration has been still ongoing [ McFadden et al , ]; however, the GSR results (in particular, the flux rope axial orientation and shape) do not significantly change.…”

“…The flux rope boundary overplotted by a dashed magenta curve onto Figure c is defined as a surface where the reconstructed axial field strength is 50% relative to the core field value. This definition is the same as Hara et al []. Using the same methodologies as taken by, e.g., Hara et al [, , ], we estimated the spatial scales of the observed ionospheric flux rope.…”

“…On the other hand, MAVEN enables the measurements in various plasma regimes including the upstream solar wind, magnetosheath, induced magnetosphere, and down to the Martian ionosphere [ Jakosky et al , ]. The MAVEN comprehensive particle and field instruments allow us to reveal unprecedented behaviors of the Martian flux ropes [ Hara et al , ].…”