Electron Densities in the Ionosphere of Mars: Comparison of MAVEN/ROSE and MAVEN/LPW Measurements

Several different instrument types have been widely used to measure the density of plasma in solar system ionospheres. However, limitations in spatial and temporal coverage have prevented efforts to directly compare electron density measured by different kinds of instrument in order to assess whether systematic errors exist in such measurements. Here, we exploit the excellent observational coverage provided at Mars by the MAVEN spacecraft to compare numerous electron density measurements from two instruments, the Radio Occultation Science Experiment (ROSE, a remote sensing investigation) and Langmuir Probe and Waves (LPW, an in situ instrument). For dusk local times, we find that systematic contrasts between ROSE and LPW electron density measurements are less than 4 x 10(3) cm(-3). As this limit is only modestly greater than the intrinsic measurement uncertainty on ROSE electron density observations, we conclude that any systematic error present in either data set is smaller than the instrumental accuracies. Differences are larger, between 8 x 10(3) and 1.2 x 10(4) cm(-3), at dawn local times. From the differences, ratios, and percentage difference between the ROSE and LPW densities, we postulate that electron densities are more variable in the dawn ionosphere than in the dusk ionosphere.