Temporal Variability of Waves at the Proton Cyclotron Frequency Upstream from Mars: Implications for Mars Distant Hydrogen Exosphere

TL;DR

This study analyzes the temporal variability of proton cyclotron waves upstream from Mars, linking wave occurrence rates to hydrogen exosphere density changes and solar activity, suggesting waves as probes for Martian exospheric dynamics.

Contribution

It provides new observational evidence connecting wave occurrence with Martian hydrogen exosphere variations and solar activity, offering a novel method to study exospheric evolution.

Findings

Wave occurrence rates vary with solar activity and Martian seasons.

Higher wave activity correlates with increased hydrogen exosphere density.

Results support using wave observations to study Martian exospheric dynamics.

Abstract

We report on the temporal variability of the occurrence of waves at the local proton cyclotron frequency upstream from the Martian bow shock from Mars Global Surveyor observations during the first aerobraking and science phasing orbit periods. Observations at high southern latitudes during minimum-to-mean solar activity show that the wave occurrence rate is significantly higher around perihelion southern summer solstice and lower around the same hemisphere's spring and autumn equinoxes. A similar trend is observed in the hydrogen (H) exospheric density profiles over the Martian South Pole obtained from a model including UV thermospheric heating effects. In spite of the complexity in the ion pick-up and plasma wave generation and evolution processes, these results support the idea that variations in the occurrence of waves could be used to study the temporal evolution of the distant Martian H corona and its coupling with the thermosphere at altitudes currently inaccessible to direct measurements.