Time-dispersed ion signatures observed in the Martian magnetosphere by MAVEN

Abstract

Mars Atmosphere and Volatile EvolutioN mission's (MAVEN) high-cadence measurements reveal the frequent occurrence of ion energy dispersion events inside the Martian magnetosphere. The systematics of observed dispersion signatures suggest time dispersion of a broad source spectrum over a flight distance of a few thousand kilometers and disfavor mechanisms involving spatial dispersion. Pickup of heavy planetary ions in strong variable electric fields provides one potential mechanism that could produce the observed time dispersion signatures. The periodicity of many observed dispersion signatures, with frequencies near the upstream proton cyclotron frequency, suggests a possible role for low-frequency plasma waves in accelerating the observed ions from a source near the induced magnetospheric boundary to the observation location inside the magnetospheric tail lobes. The observed dispersion signatures may provide a new way to track the flow of energy from the upstream region through the magnetosphere and the role of waves in driving the escape of ions from the atmosphere.