Comparative Measurements of Ionospheres at Mars and Earth: MGS, MEX, MRO, MAVEN and Ionosondes

Observations of the martian ionosphere are now second in number only to those made on Earth. Using MGS profiles and four terrestrial ionosonde stations, we show that the maximum electron densities of the main molecular-ion/electron plasma layers at Earth (E-layer) and Mars (M2-layer) are highly correlated under "same-day" solar irradiance conditions—even though they are produced by different portions of the solar irradiance. The integral with height of an electron density profile Ne(h) yields the parameter total electron content (TEC). There are multiple ways of observing the total electron content (TEC) at Mars using radar methods on two satellites (MARSIS/MEX and SHARAD/MRO). We have conducted a case study comparing the TEC from SHARAD on the same day and approximately the same location as MAVEN observations of ionospheric profiles from two in-situ instruments—the neutral gas and ion mass spectrometer (NGIMS) and the Langmuir Probe and Wave (LPW) sensor. Agreement of TEC derived from NGIMS and LPW with past statistical studies from MARSIS, as well as same day sampling from SHARAD, indicate that multiple ways exist for MAVEN instruments to assess reliably the cold plasma reservoir capable of escape from Mars.