Martian Meteoric Metals: An intercomparison of MAVEN Observations and PCM-Mars Simulations

Before NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft entered Mars’ orbit in 2014, meteoric metals had not been directly measured in a planetary atmosphere beyond Earth. MAVEN’s Imaging Ultraviolet Spectrograph (IUVS) has since measured a persistent layer of Mg⁺ in the Martian upper atmosphere. Metal species are injected into the atmosphere via ablation at altitudes where the pressure is ~1 μbar; the peak of the Mg⁺ layer varies over the Martian year due to changes in atmospheric density caused by the deposition and sublimation of CO₂ at the poles. During Mars’ close encounter with the Oort cloud comet, Siding Spring, in October 2014, the IUVS instrument could also observe Mg, Fe, and Fe⁺. Neutral Mg was observed to decay at rates much faster than predicted and global models simulate nominal densities above the detection limit of the IUVS instrument, suggesting an incomplete understanding of Mg chemistry. The MAVEN mission included nine ‘Deep Dip’ campaigns, during which the nominal altitude range of the spacecraft was extended to include altitudes as low as 125 km. These week-long campaigns were designed to sample a variety of locations, local times, and solar longitudes, and offered the unique opportunity to measure Mg⁺, Fe⁺, and Na⁺ in-situ with the Neutral Gas and Ion Mass Spectrometer (NGIMS).

 

This study investigates the variability of Mars’ meteoric metal layers by comparing MAVEN IUVS and NGIMS observations with PCM-Mars simulations of the deep dip campaigns and the passing of Siding Spring. The PCM-Mars is a 3D numerical model of the Martian atmosphere, simulating atmospheric chemistry, circulation, temperature, and dust from the surface to the exobase. For the deep dip simulations, the Leeds Chemical Ablation Model (CABMOD) and the Meteoric Input Function (MIF) of Carrillo-Sánchez et al. (2022) were used to model the injection of MgO, Mg⁺, Fe, Fe⁺, Na, Na⁺, SiO, and Si⁺; we implemented a Siding Spring MIF to investigate the missing neutral Mg. For all simulations we have implemented a 4-metal chemistry scheme modelling Mg, Fe, Na, and Si reactions. This intercomparison of MAVEN observations and PCM-Mars simulations is vital to constraining global models and understanding the key drivers controlling the variability of Mars’ metal layers.

 

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., Schneider, N.M., Evans, J.S., Plane, J.M.C, Carrillo-Sánchez, J. D, Jain, S.K., Deighan, J.I., and Yelle, R.V. The Impact of Comet Siding Spring’s Meteors on the Martian Atmosphere and Ionosphere, JGR. Planets., 123(10): 2613-2627, doi:10.1029/2018JE005750, 2018.

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.