Statistical Characteristics of Nighttime ULF Waves Observed on the Surface of Mars by InSight

Abstract

Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) Fluxgate Magnetometer returned data from the Martian surface throughout the course of the InSight mission, between November 2018 and May 2022. Ultra-low frequency (ULF) electromagnetic waves are commonly observed by InSight during nighttime hours. We present a collection of 444 nighttime ULF wave events with characteristic frequencies ranging from 1 to 16 mHz (periods from about 1 to 17 min), with a median frequency of about 7 mHz (period of about 140 s). Ultra-low frequency wave activity is found across all nighttime hours, but the activity is more commonly observed after midnight local time. A subset of 104 InSight ULF wave events occur while Mars Atmosphere and Volatile EvolutioN (MAVEN) is located in the solar wind. During these events, the interplanetary magnetic field (IMF) deviates from its nominally expected orientation. We suggest that ULF waves are likely produced in the Martian magnetosphere by at least two different mechanisms and that the occurrence of the ULF waves on the surface is sensitive to the solar wind interaction with the Martian crustal fields. Further measurements by lander or orbiter missions will provide more information about the origin of ULF waves, how they reach the surface during the nighttime, and whether or not ULF waves can be used to perform magnetic sounding to study the subsurface of Mars.