Climatology of Mars Topside Ionosphere during Solar Cycles 24 and 25 using MAVEN Dataset of 2015-2024

TL;DR

This study analyzes MAVEN data from 2015-2024 to reveal how the Martian topside ionosphere varies with solar activity, showing higher densities during solar maximum and differences between dayside and nightside ionization.

Contribution

First long-term climatology of Mars topside ionosphere across Solar Cycles 24 and 25 using MAVEN data, highlighting solar activity effects on ionospheric densities and structure.

Findings

Higher ionospheric densities during solar maximum.

Daytime densities 1-2 orders higher than nightside.

Electron and molecular ion densities increase significantly during maxima.

Abstract

The Mars ambient space environment evolves with the varying solar activity. Understanding the Martian space environment, particularly the topside ionosphere across different phases of Solar Cycles (SC) 24 \& 25 remains a key research gap in planetary ionospheric science. In this study, we utilized the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission data (150-500 km) from Martian years 32-38 (2015-2024) during solar quiet-time. This study investigated the behavior of topside ionosphere (e-, CO2+, O2+, NO+, OH+, O+, N+ \& C+) across different phases of SC over the northern hemisphere. A significant variation in ionosphere is observed over low-latitude (0-30{\deg}N) with higher densities compared to mid-latitude (31-60{\deg}N) across SC. Additionally, we found that the Martian northern ionospheric densities were highest during solar maximum phase on both dayside and nightside compared to low active phases. The dayside densities were approximately 1-2 orders higher compared to those on the nightside. The electron and molecular ions densities increased by factors of 1-5 and 1-13, respectively. While O+ ion density was enhanced by nearly 2-2.5 times, along with an upliftment of 40-50 km in the peak height. The enhanced dayside densities are attributed to the elevated solar irradiance (1.4-2 times) and varying solar wind flux. Furthermore, the enhanced day-to-night plasma transport and elevated solar electron flux during maxima, higher by 33-66\% than during low-activity, can contribute to the increased nightside ionization. This work, for the first time, uses long-term MAVEN datasets across the descending-to-maxima phases of SC to reveal climatology of Martian topside ionosphere.