An Overview of the MAVEN Deep Dip Campaigns

Abstract MAVEN's 10 Deep Dip campaigns, when periapsis altitude was lowered from 150 km to 120 km for short periods in 2015–2019, have made major contributions to current understanding of the thermosphere and ionosphere of Mars, as well as of present escape and implications for past climate. Yet the available literature on the Deep Dip campaigns is fragmentary, naturally tending to emphasize the scientific results of the individual research project being reported. In order to view the Deep Dip campaigns in their totality, to integrate their main findings coherently, and to identify promising opportunities for further exploitation of their data, here we present a comprehensive overview of MAVEN's Deep Dip campaigns. For the thermosphere, MAVEN Deep Dip observations have revealed: the homopause altitude and its notable variability; gravity waves and their dissipation; thermospheric composition, its day‐to‐day variability (exemplified by the O/C ratio), and its response to changing solar irradiance; and the thermal structure of the lower thermosphere between the cold mesopause and the hot, isothermal upper thermosphere. For the ionosphere, MAVEN Deep Dip observations have revealed: ionospheric composition, its day‐to‐day variability (exemplified by the /C ratio), and its response to changing solar irradiance; the dependence of ionization efficiency upon altitude; electron and ion temperatures; and the presence of multiple species of metal ions. Solar conditions and atmospheric dust conditions, relevant observations by MAVEN remote sensing instruments and by other missions, and potential avenues for future analyses of Deep Dip data are also addressed.