6 research outputs found
Meteoric Metal Chemistry in the Martian Atmosphere
Recent measurements by the Imaging Ultraviolet Spectrograph (IUVS) instrument on NASA's Mars Atmosphere and Volatile EvolutioN mission show that a persistent layer of Mgâș ions occurs around 90 km in the Martian atmosphere but that neutral Mg atoms are not detectable. These observations can be satisfactorily modeled with a global meteoric ablation rate of 0.06 t solâ»Âč, out of a cosmic dust input of 2.7 ± 1.6 t solâ»Âč. The absence of detectable Mg at 90 km requires that at least 50% of the ablating Mg atoms ionize through hyperthermal collisions with COâ molecules. Dissociative recombination of MgOâș.(COâ)n cluster ions with electrons to produce MgCOâ directly, rather than MgO, also avoids a buildup of Mg to detectable levels. The meteoric injection rate of Mg, Fe, and other metalsâconstrained by the IUVS measurementsâenables the production rate of metal carbonate molecules (principally MgCOâ and FeCOâ) to be determined. These molecules have very large electric dipole moments (11.6 and 9.2 Debye, respectively) and thus form clusters with up to six HâO molecules at temperatures below 150 K. These clusters should then coagulate efficiently, building up metal carbonateârich ice particles which can act as nucleating particles for the formation of COââice clouds. Observable mesospheric clouds are predicted to occur between 65 and 80 km at temperatures below 95 K and above 85 km at temperatures about 5 K colder
Localized Ionization Hypothesis for Transient Ionospheric Layers
The persistent twoâpeaked vertical structure of the Martian ionosphere is created by extreme and far ultraviolet radiation whose energies respectively determine their ionization altitude. A third lowâaltitude transient layer (previously referred to as M3 or Mm) has been observed by radio occultation techniques and attributed to meteor ablation. However, recent remote sensing and inâsitu observations disfavor a meteoric origin. Here we propose an alternative hypothesis for these apparent layers associated with impact ionization from penetrating solar wind ions, previously observed as proton aurora. Localized ionization, occurring nonâglobally at a given altitude range, breaks the symmetry assumed by the radio occultation technique, and creates electron layers apparently lower in the ionosphere than their true altitude. This may occur when the upstream bowshock is altered by a radial interplanetary magnetic field configuration, which allows the solar wind to penetrate directly into the thermosphere. This localized ionization hypothesis provides an explanation for apparent layersâ wide variation in heights and their transient behavior. Moreover, this hypothesis is testable with new observations by the Mars Atmospheric and Volatile EvolutioN (MAVEN) Radio Occultation Science Experiment (ROSE) in future Mars years. This hypothesis has implications for the ionospheres of Venus and Titan, where similar transient layers have been observed
A Modeling Study of the Seasonal, Latitudinal, and Temporal Distribution of the Meteoroid Mass Input at Mars: Constraining the Deposition of Meteoric Ablated Metals in the Upper Atmosphere
This study provides a comprehensive description of the deposition of meteor-ablated metals in the upper atmosphere of Mars, accounting for the temporal, vertical, latitudinal, and seasonal distribution. For this purpose, the Leeds Chemical Ablation Model is combined with a meteoroid input function to characterize the size and velocity distributions of three distinctive meteoroid populations around Marsâthe Jupiter-family comets (JFCs), main-belt asteroids, and Halley-type comets (HTCs). These modeling results show a significant midnight-to-noon enhancement of the total mass influx because of the orbital dynamics of Mars, with meteoroid impacts preferentially distributed around the equator for particles with diameters below 2000 ÎŒm. The maximum total mass input occurs between the northern winter and the first crossing of the ecliptic plane with 2.30 tons solâ1, with the JFCs being the main contributor to the overall influx with up to 56% around Mars' equator. Similarly, total ablated atoms mainly arise from the HTCs with a maximum injection rate of 0.71 tons solâ1 spanning from perihelion to the northern winter. In contrast, the minimum mass and ablated inputs occur between the maximum vertical distance above the ecliptic plane and aphelion with 1.50 and 0.42 tons solâ1, respectively. Meteoric ablation occurs approximately in the range altitude between 100 and 60 km with a strong midnight-to-noon enhancement at equatorial latitudes. The eccentricity and the inclination of Mars' orbit produces a significant shift of the ablation peak altitude at high latitudes as Mars moves toward, or away, from the northern/southern solstices
Martian Meteoric Mg+: Atmospheric Distribution and Variability From MAVEN/IUVS
Since the discovery of atmospheric Mg+ on Mars in 2015 by the Mars Atmosphere and Volatile Evolution mission, there have been almost continuous observations of this meteoric ion layer in a variety of seasons, local times, and latitudes. Here, we present the most comprehensive set of observations of the persistent metal ion layer at Mars, constructing the first grand composite maps from pooled medians of subsamples of a metallic ion species. These maps demonstrate that Mg+ appears in almost all conditions when illuminated, with peak density values varying between 100 and 500 cmâ3, dependent on season and local time. There exists significant latitudinal variation within a given season, indicating that Mg+ is not simply an inert tracer, but may instead be influenced by the meteoric input distribution and/or atmospheric dynamics and chemistry. Geographic maps of Mg+ density as a function of latitude and longitude indicate the influence of atmospheric tides, and there is no apparent correlation with remnant crustal magnetic fields. This work also presents counter-intuitive results, such as a reduction of Mg+ ions in the northern hemisphere during Northern Winter in an apparent correlation with dust aerosols
Annual appearance of hydrogen chloride on Mars and a striking similarity with the water vapor vertical distribution observed by TGO/NOMAD
Hydrogen chloride (HCl) was recently discovered in the atmosphere of Mars by two spectrometers onboard the ExoMars Trace Gas Orbiter. The reported detection made in Martian Year 34 was transient, present several months after the global dust storm during the southern summer season. Here, we present the full data set of vertically resolved HCl detections obtained by the NOMAD instrument, which covers also Martian year 35. We show that the particular increase of HCl abundances in the southern summer season is annually repeated, and that the formation of HCl is independent from a global dust storm event. We also find that the vertical distribution of HCl is strikingly similar to that of water vapor, which suggests that the uptake by water ice clouds plays an important role. The observed rapid decrease of HCl abundances at the end of the southern summer would require a strong sink independent of photochemical loss