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

Abstract

We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of a giant magnetic flux rope in the Martian dayside ionosphere. The flux rope was observed at an altitude of <300 km, downstream from strong subsolar crustal magnetic fields. The peak field amplitude was ∼200 nT, resulting in the largest difference between the observed magnetic field strength and a model for crustal magnetic fields of the entire MAVEN primary science phase. MAVEN detected planetary ions, including H+, O+, and O2+, across the structure. The axial orientation estimated for the flux rope indicates that it likely formed as a result of interactions between the local crustal and overlaid draped interplanetary magnetic fields. Pitch angle distributions of ionospheric photoelectrons imply that this structure is connected to the Martian upper atmosphere. However, the flux rope is not present in observations at the next commensurable orbit crossing (approximately two Martian days later), implying that it eventually detaches from the atmosphere and is carried downstream. The flux rope observations occurred during an interplanetary coronal mass ejection event at Mars, suggesting that the disturbed upstream state played a role in allowing the interplanetary magnetic field to penetrate deeper into the Martian ionosphere than is typical, allowing the formation of the flux rope.

On the origins of magnetic flux ropes in near‐Mars magnetotail current sheets

“…For example, their observed duration is about several tens of seconds with a peak field ranging between ∼10 and 25 nT. Multiple ion species including H + , O + , and O + 2 are simultaneously recorded during their encounters that is consistent with the previous MAVEN observations [Hara et al, , 2016[Hara et al, , 2017. However, it should be noted that the flux ropes with ≥ 60 ∘ tend to be observed in a series of multiple flux rope signatures across a single magnetotail current sheet as shown in Figure 3.…”

“…Alternatively, we can explore the second possibility that does not necessitate magnetotail reconnection: transport of flux ropes that are originally generated in the dayside ionosphere through plasma instabilities such as helical kink, Kelvin‐Helmholtz instabilities [e.g., Elphic and Russell , ; Wolff et al , ; Ruhunusiri et al , ], and magnetic reconnection in consequence of interactions between the IMF and crustal fields [e.g., Hara et al , , ], or dayside magnetic reconnection analogous to the terrestrial flux transfer events [see, e.g., Hasegawa , , and references therein]. As illustrated in Figure b, these helical draped magnetic field lines can be subsequently transported into the nightside magnetotail forming the current sheet, allowing spacecraft to detect them as flux ropes embedded in the magnetotail current sheets.…”

“…Indeed, these helical flux rope structures are quite common in the Martian plasma environment [e.g., Cloutier et al, 1999;Vignes et al, 2004;Brain et al, 2010;Briggs et al, 2011;Hara et al, 2014aHara et al, , 2014b. Some researchers proposed that the ionospheric flux ropes are formed by magnetic reconnection between crustal magnetic field themselves Beharrell and Wild, 2012] or between the crustal field and the overlaid IMF [Hara et al, 2014b[Hara et al, , 2017; however, the physical mechanisms responsible for generating flux ropes in the Martian induced magnetotail remain poorly understood. , viewed from the current sheet based minimum variance analysis (CS-B MVA ) coordinates.…”

Magnetic Reconnection on Dayside Crustal Magnetic Fields at Mars: MAVEN Observations

“…Meanwhile, it remains elusive whether magnetic reconnection operates on the dayside of Mars, and if so, how it dictates the structure and dynamics of the Martian magnetosphere. As summarized by Halekas et al (2009), current sheets capable of reconnection can be generated on the dayside of Mars in multiple possible configurations: (i) between the interplanetary magnetic field (IMF) on both sides (equivalent cases are considered for comets and Venus (Niedner & Brandt, 1978;Vech et al, 2016)), (ii) between the IMF on one side and crustal field on the other (Hara et al, 2014(Hara et al, , 2016Krymskii et al, 2002), and (iii) between the crustal field on both sides (Beharrell & Wild, 2012;Brain et al, 2010). Though effects and products of dayside reconnection at Mars have been discussed in the aforementioned literature, there have been few reports on direct measurements of in situ reconnection signatures (such as accelerated plasma flows and Hall magnetic fields within current sheets; e.g., Paschmann et al, 2013).…”

Survey of magnetic reconnection signatures in the Martian magnetotail with MAVEN

“…Injection and trapping of electrons on closed magnetic field lines have been observed near the Martian crustal magnetic fields [ Brain et al , ; Ulusşen and Linscott , ; Harada et al , ; Xu et al , ]. Magnetic flux ropes can be formed by reconnection between draped interplanetary fields in the induced tail current sheets, between crustal and draped fields, or between neighboring crustal fields [ Brain et al , ; Briggs et al , ; Beharrell and Wild , ; Eastwood et al , ; Hara et al , , ; Soobiah et al , ; DiBraccio et al , ]. In order to evaluate the role of reconnection in their generation processes, it is necessary to characterize the basic properties of magnetic reconnection at Mars based on in situ observations of particle and field signatures around X lines.…”