First measurements of composition and dynamics of the Martian ionosphere by MAVEN's Neutral Gas and Ion Mass Spectrometer

Abstract

We report the results of the observations of the ionosphere of Mars by the Neutral Gas and Ion Mass Spectrometer. These observations were conducted during the first 8 months of the Mars Atmosphere and Volatile EvolutioN mission (MAVEN). These observations revealed the spatial and temporal structures in the density distributions of 22 ions: H2+, H3+, He+, O2+, C+, CH+, N+, NH+, O+, OH+, H2O+, H3O+, N2+/CO+, HCO+/HOC+/N2H+, NO+, HNO+, O2+, HO2+, Ar+, ArH+, CO2+, and OCOH+. Dusk/dawn and day/night asymmetries in the density distributions were observed for nearly all ion species. Additionally, high‐density fluctuations were detected on the nightside and may reflect the effect of the partial screening of the atmosphere of Mars by the weak intrinsic magnetic field of the planet. The two first MAVEN “deep dip” campaigns were used to investigate the location of the primary ion peak. This peak was detected at 190 km near the terminator but was below the spacecraft altitude of 130 km near the subsolar point.

Hot oxygen escape from Mars: Simple scaling with solar EUV irradiance

“…The CO 2 + density is about 10% of the O 2 + density near an altitude of 200 km. This has been observationally confirmed by measurements made by the Neutral Gas and Ion Mass Spectrometer (NGIMS) experiment on board the MAVEN spacecraft [ Benna et al ., ].…”

“…Hence, for the most part, almost any ion produced from any neutral species will end up as O 2 + , as long as there is sufficient CO 2 and O to react with. Current ionospheric models can explain the observed major ion composition [ Fox et al ., ; Benna et al ., ; Withers et al ., …], but there is also a rich minor ion chemistry [cf. Matta et al ., ; Fox et al ., ], which we will not discuss.…”

“…The transition between the photochemically controlled ionosphere and a transport‐dominated ionosphere can be estimated by comparing the plasma transport time ( τ T ) to the photochemical lifetime of the major ion species. MAVEN ionospheric data [e.g., Mahaffy et al ., ; Benna et al ., ] and ionospheric models of Mars [e.g., Withers et al ., ] indicate that under most circumstances, O 2 + remains the major ion species up to about 300 km. The chemical lifetime of O 2 + is given by the dissociative recombination time: τ DR = 1/( αn e ).…”

The Impact of Crustal Magnetic Fields on the Thermal Structure of the Martian Upper Atmosphere

“…σ p could be obtained from known information of the ion-neutral and electronneutral collision frequencies based on the NGIMS CO 2 measurements and the electron temperature measurements made by the MAVEN Langmuir Probe and Waves instrument (Ergun et al 2015), the ion and electron conductivities based on the NGIMS O 2 + measurements in the open-source ion mode (Benna et al 2015), and finally the ion and electron gyrofrequencies based on the magnetic field measurements made by the MAVEN Magnetometer (Connerney et al 2015). Detailed calculations yield S p below 0.02Sm −1 for DD2 and below 0.01Sm −1 for DD4, both over regions with strong crustal magnetic fields.…”

Ion Heating in the Martian Ionosphere

“…Ion velocity distributions relative to the local magnetic field from the event shown in Figure are shown in Figure . Figures a–f show data for O + ; Figures g–l show data for O (these are the primary ion species at these altitudes in the dayside ionosphere, e.g., Benna et al, ). The horizontal and vertical axes show ion velocity parallel and perpendicular to the local magnetic field, respectively, where positive horizontal direction is along the field.…”