Joseph M. Grebowsky

MAVEN observations of the response of Mars to an interplanetary coronal mass ejection

Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.

Meteoric magnesium ions in the Martian atmosphere

From a thorough modeling of the altitude profile of meteoric ionization in the Martian atmosphere we deduce that a persistent layer of magnesium ions should exist around an altitude of 70 km. On the basis of the estimated meteoroid mass flux density, a peak ion density of ∼ 10 4 ions cm -3 is predicted. Allowing for the uncertainties in all of the model parameters, this value is probably within an order of magnitude of the correct density. Of these parameters, the peak density is most sensitive to the meteoroid mass flux density which determines the source function for Mg from the ablating meteoroids. Unlike the terrestrial case, where the metallic ion production is dominated by charge-exchange of the deposited neutral Mg with the ambient ions, Mg + in the Martian atmosphere is produced predominantly by photoionization. The low ultraviolet absorption of the Martian atmosphere makes Mars an excellent laboratory in which to study meteoric ablation. Resonance lines in the ultraviolet that cannot be seen in the spectra of terrestrial meteors may be visible to a surface observatory in the Martian highlands.

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

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.

Early MAVEN Deep Dip campaign reveals thermosphere and ionosphere variability

The Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above the well-mixed atmosphere, the layer of peak extreme ultraviolet heating and primary reservoir for atmospheric escape. In situ measurements of the upper atmosphere reveal previously unmeasured populations of neutral and charged particles, the homopause altitude at approximately 130 kilometers, and an unexpected level of variability both on an orbit-to-orbit basis and within individual orbits. These observations help constrain volatile escape processes controlled by thermosphere and ionosphere structure and variability.

Initial results from the MAVEN mission to Mars

The Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars orbiter has been gathering information on the Mars upper atmosphere, ionosphere, and solar and solar wind interactions since its orbit insertion in September 2014. MAVENs science goals are to understand processes driving the escape of atmospheric gases to space at the present epoch, and their variations with solar and local heliospheric conditions together with geographical and seasonal influences. This introduction and the accompanying articles provide a selection of key results obtained up to the time of writing, including measurements of the overall geometry and variability of the Martian magnetosphere, upper atmosphere, and ionosphere and their responses to interplanetary coronal mass ejections and solar energetic particle influxes. The ultimate goal is to use these results to determine the integrated loss to space through time and its role in overall Mars atmosphere evolution.

Do meteor showers significantly perturb the ionosphere

More than 40 rocket flights through the main meteoric ionization layer, which peaks near 95 km, have sampled the meteoric metallic ion concentrations. Five of these flights were conducted during or near the peak times of a meteor shower. In each of the latter studies the observed meteoric ion concentrations were assumed to be a consequence of the shower. These measurements were not complemented by baseline observations made for similar ionospheric conditions immediately before the shower and no rigorous quantitative comparisons were made using average non-shower distributions. In order to further investigate the impact of the shower on the ionosphere, all published ion concentration altitude profiles obtained from sounding rockets in the meteoric ionization regime have been scanned to develop a digital data base of meteoric ion concentrations. These data are used to provide the first empirical altitude profile of the metallic ions. The average observed Mg+ concentrations are lower than those yielded by the most comprehensive model to date (McNeil et al., 1996). This compiled ensemble of data provides supporting evidence that meteor showers do have a significant impact on the average ionosphere composition. Although there is much variability in the observed meteoric layers, the peaks in the total metallic ion concentrations at mid-latitudes, on the dayside, observed during meteor showers had concentrations comparable to, or exceeding, the highest concentrations measured in the same altitude regions during non-shower periods.

Metallic ions in the upper atmosphere of Mars from the passage of comet C/2013 A1 (Siding Spring)

We report the first in situ detection of metal ions in the upper atmosphere of Mars resulting from the ablation of dust particles from comet Siding Spring. This detection was carried out by the Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution Mission. Metal ions of Na, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and possibly of Si, and Ca, were identified in the ion spectra collected at altitudes of ~185 km. The measurements revealed that Na+ was the most abundant species, and that the remaining metals were depleted with respect to the CI (type 1 carbonaceous Chondrites) abundance of Na+. The temporal profile and abundance ratios of these metal ions suggest that the combined effects of dust composition, partial ablation, differential upward transport, and differences in the rates of formation and removal of these metal ions are responsible for the observed depletion.

Location and source of ionospheric high latitude troughs

Abstract One prominent feature of the high latitude topside ionosphere is the existence of sharp latitudinal depletions in the total ion (electron) concentrations within the auroral/cusp regions. These high latitude troughs, as seen by the Bennett ion mass spectrometer observations on the satellite OGO 6 at altitudes between 400 and 1100km correspond to depletions in the atomic ions which are accompanied by localized enhancements of the minor molecular ion densities. All of the high latitude troughs traversed by OGO 6 (1969–1970) were recorded and the average invariant latitude-magnetic local time (M.L.T.) distribution was determined. The troughs on the average were found at all local times to be in the vicinity of the auroral oval and to move equatorward in response to increasing magnetic activity. The average trough location was compared to the average polar cap boundary as defined by the convection electric field reversal and the electron trapping boundary as well as to the maximum horizontal magnetic disturbance associated with the large scale field aligned currents. The high latitude troughs on the average best followed the maximum magnetic disturbance distribution. It is concluded that the troughs are the result predominantly of enhanced chemical 0+ losses in regions with high convection velocities.

Thermal ion perturbations observed in the vicinity of the Space Shuttle

Abstract During the Spacelab-2 Shuttle mission the University of Iowa Plasma Diagnostic Package (PDP) probed the plasma environment of the Space Shuttle by maneuvers at the end of the extended Remote Manipulator System (RMS) arm. Also the PDP was operated as a free flying satellite which remained in the vicinity of the Shuttle as the Shuttle was maneuvered about it. During this portion of the mission, the Bennett thermal ion mass spectrometer on the PDP measured some distinctive effects of the large and gaseous emitting Shuttle upon the ambient thermal plasma environment. Within the open cargo bay when thrusters were not firing there was typically an absence of measurable thermal ions when the bay was in the wake of the spacecraft. Just above the top of the bay when traces of ions are detected in the wake the dominant ion was the contaminant water. When the PDP was released in the wake of the Shuttle and moved away, the spin modulation of the ion flux into the spectrometer was initially different for the O + and H 2 O + ions. The O + ions were streaming into the spectrometer from the spacecraft velocity direction whereas the water ions were flowing from a direction as much as 77° from this. The concentration of water ions in the near wake decreased with increasing distance, becoming less than the predominant ion O + at wake distances of the order of 30 m. However, traces of contaminant ions were present as far as the maximum distance of several hundred meters explored by the free-flying PDP. The neutral gases from the Shuttle extend in all directions as was shown by the presence of water ions, not only in the immediate vicinity of the Shuttle and in its wake but also even several hundred meters upstream. The presence of contaminant NO and O + 2 ions brings into question whether reliable ambient ion measurements can be made from the Shuttle.

Comparisons of modeled N+, O+, H+, and He+ in the midlatitude ionosphere with mean densities and temperatures from Atmosphere Explorer

In this study, Atmosphere Explorer data and model results from the ion and electron temperature and the density of N+, O+, H+, and He+ between 120 and 1400 km altitude are compared for two midlatitude ranges (L=2 and L=4), noon and midnight local time, winter and summer, at solar minimum. The data for the heavy atomic ions (O+ and N+) show that their densities are greater at noon than at midnight for a given season and greater in summer than winter for given local time. There is only a weak latitudinal variation in the density of these ions. The data show that the light ion (H+ and He+) densities are greater at midnight than at noon and are generally greater in winter than summer. There is a strong latitudinal variation of the light ion densities, with the densities decreasing with increasing latitude. The model densities are in good agreement with the AE densities for N+, O+, and H+. Model He+ densities are lower, by a factor of 2 or more than the measured densities. Model ion and electron temperatures agree well with the measured temperatures with only a modest increase in plasmaspheric heating. 44 refs., 14 figs.