Investigating Martian Meteoric Metal Variability Through the Intercomparison of MAVEN/NGIMS Deep Dip Data and PCM-Mars Simulations.

In 2014, NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) satellite made the first direct atmospheric measurements of planetary meteoric metals beyond Earth. A persistent layer of Mg⁺ was observed at ~90 km via the remote sensing of the Mg⁺ dayglow emission at 280 nm using MAVEN’s Imaging Ultraviolet Spectrograph (IUVS). This was first reported by Crismani et al. (2017) and the observed variability of the Mg⁺ layer was investigated by Crismani et al. (2023). Metallic species are injected into the Martian upper atmosphere via meteoric ablation, where the constituents of interplanetary dust particles (IDPs) are heated by thermal collisions and injected as metallic vapours. Ablation starts to occur at altitudes where the pressure is ~1 μbar and so the altitude of the Mg⁺ layer exhibits seasonal variability due to changes in the aerobraking altitude. On Mars the atmospheric density varies significantly over the Martian year due to the sublimation and deposition of CO₂ at the polar caps.

 

The MAVEN mission has included nine ‘Deep Dip’ campaigns in which the altitude of the spacecraft was lowered from its nominal altitude range of 150-500 km to include altitudes as low as 125 km. The timing and locations of these week-long campaigns were designed such that measurements could be made over a variety of local times, longitudes, latitudes, and solar longitudes. These Deep Dip campaigns offer the unique opportunity to make in situ measurements of meteoric metal species using the Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument. NGIMS has measured a variety of meteoric metal ions including Mg⁺, Fe⁺, and Na⁺. This study investigates the diurnal, seasonal, and latitudinal variability of these metallic species through an intercomparison of NGIMS Deep Dip data and Laboratoire de Météorologie Dynamique (LMD) Mars Planetary Climate Model (PCM) simulations. The PCM-Mars is a 3D numerical model which simulates the Martian atmosphere from the surface to the exobase modelling temperatures, dust, winds, and photochemistry, as well as neutral and ion-molecule chemical reactions.  The Leeds Chemical Ablation Model (CABMOD) of Vondrak et al. (2008) and the Meteoric Input Function (MIF) of Carrillo-Sanchez et al. (2022) have been used to simulate the injection of these metallic vapours and a full chemistry scheme of Mg, Fe, and Na reactions has been incorporated into the PCM-Mars.

 

Examination of the NGIMS data has shown anomalous metallic isotopic ratio values, highlighting how it is important to be cautious when analysing this data. To ensure reliable profiles are extracted from the Deep Dip dataset, this work implements a data filter which identifies orbits in which the expected isotopic ratios are observed. Generally, metals with higher atomic masses and orbits during night-time hours provide more reliable data. This intercomparison of NGIMS Deep Dip data and PCM-Mars simulations with metal chemistry is integral to constraining global models and understanding the forces driving variability in the metal layers of the Martian upper atmosphere.

 

References:

Crismani, M.M.J., Schneider, N.M., Plane, J.M.C., Evans, J.S., Jain, S.K., Chaffin, M.S., Carrillo-Sánchez, J. D., Deighan, J.I., Yelle, R.V., Stewart, A.I.F., McClintock, W., Clarke, J., Holsclaw, G.M., Stiepen, A., Montmessin, F., and Jakosky, B.M. Detection of a persistent meteoric metal layer in the Martian atmosphere, Nat. Geosci., 10(6): 401-405, doi:10.1038/ngeo2958, 2017.

Crismani, M.M.J., Tyo, R.M., Schneider, N.M., Plane, J.M.C., Feng, W., Carrillo-Sánchez, J. D., Villanueva, G.L., Jain, S., Deighan, J., and Curry, S. Martian Meteoric Mg⁺: Atmospheric Distribution and Variability From MAVEN/IUVS, J. Geophys. Res. - Planets, 128(1): e2022JE007315, doi:10.1029/2022JE007315, 2023.

Vondrak, T., Plane, J. M. C., Broadley, S., and Janches, D. A chemical model of meteoric ablation, Atmos. Chem. Phys., 8(23): 7015–7031, doi:10.5194/acp-8-7015-2008, 2008.

Carrillo-Sánchez, J. D., Janches, D., Plane, J.M.C., Pokorný, P., Sarantos, M., Crismani, M.M.J., Feng, W., and Marsh, D.R. 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, Planet. Sci. J., 3(10), art. no. 239, doi:10.3847/PSJ/ac8540, 2022.