MAVEN Survey of Magnetic Flux Rope Properties in the Martian Ionosphere: Comparison With Three Types of Formation Mechanisms

Flux ropes are a magnetic field phenomenon characterized by a filament of twisted, helical magnetic field around an axial core. They form in the Martian ionosphere via three distinct mechanisms: Boundary wave instabilities (BWI), external reconnection (ER) between the interplanetary magnetic field and the crustal anomalies, and internal reconnection (IR) of the crustal anomalies themselves. We have identified 121 magnetic flux ropes (FR) from 1900 orbits using plasma and magnetic field measurements measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and separate FR into categories based on formation mechanism by analyzing electron signatures. We find evidence for flux ropes formed via BWI, ER, and IR mechanisms which comprise 9%, 34%, and 57% of our data-set, respectively. FR formed via different mechanisms exhibit differences in location and force-free radius, indicating the formation mechanism of a FR impacts their influence on the Martian plasma environment. Plain Language Summary Mars possess localized magnetic fields that are frozen into the crust of the planet and protrude out into space. On the dayside of Mars, the crustal fields interact with the charged particles and magnetic field lines that are emanating away from the Sun known as the solar wind. The processes involved in this interaction create the Martian "magnetosphere," and can have a variety of implications on the evolution of the Martian atmosphere. One by-product of this interaction is a "magnetic flux rope," (FR) which is a twisted filament of magnetic flux and plasma. FR shows evidence for the reconfiguration of magnetic field lines within the magnetosphere, and lead to atmospheric loss at Mars. Using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we analyze 121 events in which the spacecraft encountered a FR along its orbit around Mars. This is the first study to show evidence for Martian FR having been formed via three distinct formation mechanisms. FR formed via different mechanisms exhibit differences in geographic location and size, indicating the formation mechanism of a FR impacts their influence on the Martian magnetospheric and atmospheric environment.