Carbon Ion Fluxes at Mars: First Results of Tailward Flows From MAVEN-STATIC

Characterizing C⁺ ions in the Martian ionosphere is important for understanding the history of the Martian atmosphere and surface due to its place in understanding carbon escape. Measuring minor ions, like C⁺, which are close in mass to major atmospheric ions, in this case O⁺, is difficult, requiring fitting algorithms and accurate background subtraction. Accurate measurement of these species is essential for understanding chemistry and transport in the ionosphere. In this paper, we use data from the Mars Atmospheric and Volatile EvolutioN SupraThermal And Thermal Ion Composition (MAVEN-STATIC) sensor to report the first C⁺ fluxes measured in the Martian magnetotail. We will describe a multistep method of background subtraction as well as fitting routines that are used to extract C⁺ fluxes from a 40-orbit subset of STATIC data. Our results show tailward fluxes in both optical shadow and the adjacent sunlit magnetotail at high altitudes ( > 3,000 km) and Mars-ward at low altitudes ( < 2,000 km) in shadow. These local flux values are similar to estimates of neutral carbon fluxes from photochemical escape. However, total carbon loss comparisons will require a more comprehensive study of integrated C⁺ loss over a larger data set from the Martian magnetotail.

In Situ Measurements of Thermal Ion Temperature in the Martian Ionosphere

In situ measurements of ionospheric and thermospheric temperatures are experimentally challenging because orbiting spacecraft typically travel supersonically with respect to the cold gas and plasma. We present O 2 + temperatures in Mars' ionosphere derived from data measured by the SupraThermal And Thermal Ion Composition instrument onboard the Mars Atmosphere and Volatile EvolutioN spacecraft. We focus on data obtained during nine special orbit maneuvers known as Deep Dips, during which MAVEN lowered its periapsis altitude from the nominal 150 to 120 km for 1 week in order to sample the ionospheric main peak and approach the homopause. We use two independent techniques to calculate ion temperatures from the measured energy and angular widths of the supersonic ram ion beam. After correcting for background and instrument response, we are able to measure ion temperatures as low as 100 K with associated uncertainties as low as 10%. It is theoretically expected that ion temperatures will converge to the neutral temperature at altitudes below the exobase region (∼180-200 km) due to strong collisional coupling; however, no evidence of the expected thermalization is observed. We have eliminated several possible explanations for the observed temperature difference between ions and neutrals, including Coulomb collisions with electrons, Joule heating, and heating caused by interactions with the spacecraft. The source of the energy maintaining the high ion temperatures remains unclear, suggesting that a fundamental piece of physics is missing from existing models of the Martian ionosphere.

Tidal Wave-Driven Variability in the Mars Ionosphere-Thermosphere System

In order to further evaluate the behavior of ionospheric variations at Mars, we investigate the Martian ionosphere-thermosphere (IT) perturbations associated with non-migrating thermal tides using over four years of Mars Atmosphere and Volatile Evolution (MAVEN) in situ measurements of the IT electron and neutral densities. The results are consistent with those of previous studies, namely strong correlation between the tidal perturbations in electron and neutral densities on the dayside at altitudes ~150–185 km, as expected from photochemical theory. In addition, there are intervals during which this correlation extends to higher altitudes, up to ~270 km, where diffusive transport of plasma plays a dominant role over photochemical processes. This is significant because at these altitudes the thermosphere and ionosphere are only weakly coupled through collisions. The identified non-migrating tidal wave variations in the neutral thermosphere are predominantly wave-1, wave-2, and wave-3. Wave-1 is often the dominant wavenumber for electron density tidal variations, particularly at high altitudes over crustal fields. The Mars Climate Database (MCD) neutral densities (below 300 km along the MAVEN orbit) shows clear tidal variations which are predominantly wave-2 and wave-3, and have similar wave amplitudes to those observed.