Magnetic Field Fluctuations from the Solar Wind to the Surface of Mars

Abstract

The magnetic environment of Mars is a complex and unique mix of draped interplanetary magnetic fields and localized crustal magnetic fields. The ionosphere of Mars provides an obstacle to the solar wind, which results in an induced magnetosphere. Above the ionosphere of Mars is an extended neutral exosphere which is readily ionized and these ions are picked-up by the solar wind. The interaction with the solar wind is important for understanding all layers of the Martian atmosphere. With this in mind, I developed methods for identifying and characterizing magnetic waves at a range of frequencies and altitudes. An analysis of waves from 2 Mars radii out to around 14 Mars radii was conducted to search for evidence of exospheric escape in the form of ion cyclotron waves. Instead, whistler waves were observed in the near-Mars environment. These waves are absent from Juno cruise data at 1.5 AU when Mars was more than 1 AU from Juno. This suggests these whistler waves require Mars' presence as an origin or amplifier and that Mars' plasma sphere of influence extends to at least 14 Mars radii. The lower ionosphere includes a plethora of mechanisms that influence the plasma characteristics and the generation of magnetic waves. I investigated lower altitude signals initially as a rebuttal to previous work on Martian lightning. The signals were not lightning-related, but were still of interest as these were the first 5 -16 Hz low altitude Martian waves identified. After a thorough investigation using multiple MAVEN instruments, I found that many of these waves were associated with electron precipitation. Electron precipitation is the dominant source of energy input into the Martian nightside ionosphere and is known to cause auroral activity on Earth. Waves are not present for all periods during which electron precipitation is occurring, which suggests specific conditions and/or other drivers are required to have sufficient free energy for wave emission. Further investigation is suggested. Regardless, the magnetic waves provide a unique way to search through large magnetic field datasets to find time periods of high electron energy flux into the Martian atmosphere.