Cosmic Dust Ablation and the Metallic Layers in the Upper Atmospheres of the Terrestrial Planets

This presentation concerns the impacts of cosmic dust in the atmospheres of the Earth, Mars and Venus. The input rate of cosmic dust to the Earth’s atmosphere has been very uncertain [Plane, 2012]. A recent estimate of around 28 tonnes per day globally [Carrillo-Sánchez et al., 2020] will be discussed; this was obtained using the Zodiacal Dust Cloud (or ZoDy) model [Nesvorný et al., 2011] to provide the size and velocity distributions of dust in the inner solar system, combined with the Leeds Chemical Ablation Model (CABMOD) [Vondrak et al., 2008] to determine the rate of injection of metals into the atmosphere. CABMOD is itself benchmarked using a novel Meteoric Ablation Simulator to measure the evaporation rates of metals from meteoritic particles that are flash heated, simulating atmospheric entry [Gómez-Martín et al., 2017]. The dust inputs into the atmospheres of Mars (2 t d^-1) and Venus (31 t d^-1) can now be constrained using the terrestrial input [Carrillo-Sánchez et al., 2020].

The ZoDy-CABMOD model provides the injection rates of the main meteoric constituents, as a function of height, location and time in the planet’s atmosphere. These injection profiles exhibit significant temporal and latitudinal variability depending on the eccentricity, obliquity and inclination of the planet’s orbit, as well as seasonal changes to the atmospheric density profile (particularly at high latitudes for the case of Mars [Carrillo-Sánchez et al., 2022]).

Detailed chemical networks for the four most abundant meteoric ablation elements - Mg, Fe, Si and Na - have been constructed from over 160 individual reactions involving neutral and ionized species [Plane et al., 2015]. For the terrestrial atmosphere these networks have been rigorously tested against observations of neutral and ionized metal atoms made with ground-based lidars, spaceborne spectrometers, and sub-orbital rockets. For Mars and Venus, we have included the chemistry of CO₂, both as a reactant and a third body in recombination reactions; and for Venus a detailed chlorine chemistry is added because of the very large concentration of HCl produced by volcanic emissions. Where reactions have not been studied in the laboratory, we have employed quantum chemistry calculations combined with master equation rate theory for reactions taking place on multi-well potential energy surfaces.

These chemical networks, together with the relevant metal injection rates as a function of height, location and time, have been inserted into global chemistry-climate models: the Whole Atmosphere Community Climate Model (WACCM which extends to ~140 km, and WACCM-X which extends to ~500 km) for Earth; and the Planetary Climate Models for Mars and Venus. For Mars, model simulations generally compare well against observations of metallic ions made by instruments (IUVS and NGIMS) on NASA’s MAVEN spacecraft. In particular, the diurnal, latitudinal and seasonal variations of the Mg⁺ layer centred around 95 km are captured well. However, there are several interesting differences higher in the ionosphere that are currently unexplained.

In the case of Venus, metallic species have never been observed. However, the PCM-Na model predicts that the atomic Na layer around 110 km should be observable by a terrestrial telescope with a high resolution optical spectrometer, particularly on the night side and around the dawn terminator. Metallic carbonate species are also predicted to act as ice nuclei, forming transient CO₂-ice clouds above 110 km in Venus’ atmosphere [Murray et al., 2023].  Metal carbonate clusters are also the probable nuclei of Martian noctilucent clouds [Plane et al., 2018]. Finally, a strong candidate for the mystery absorber in the Venusian clouds is iron trichloride (FeCl₃), produced by the extra-terrestrial input of Fe and volcanic HCl.   

 

Carrillo-Sánchez, J. D., J. C. Gómez-Martín, D. L. Bones, D. Nesvorný, P. Pokorný, M. Benna, G. J. Flynn, and J. M. C. Plane (2020), Cosmic dust fluxes in the atmospheres of Earth, Mars, and Venus, Icarus, 335, art. no.: 113395, doi:10.1016/j.icarus.2019.113395.

Carrillo-Sánchez, J. D., D. Janches, J. M. C. Plane, P. Pokorný, M. Sarantos, M. M. J. Crismani, W. Feng, and D. R. Marsh (2022), 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.

Gómez-Martín, J. C., D. L. Bones, J. D. Carrillo-Sánchez, A. D. James, J. M. Trigo-Rodríguez, B. Fegley, and J. M. C. Plane (2017), Novel Experimental Simulations of the Atmospheric Injection of Meteoric Metals, Astrophys. J., 836(2), art. no.: 212, doi:10.3847/1538-4357/aa5c8f.

Murray, B. J., T. P. Mangan, A. Määttänen, and J. M. C. Plane (2023), Ephemeral Ice Clouds in the Upper Mesosphere of Venus, J. Geophys. Res. – Planets, 128, art. no.: e2023JE007974.

Nesvorný, D., D. Janches, D. Vokrouhlický, P. Pokorný, W. F. Bottke, and P. Jenniskens (2011), Dynamical model for the zodiacal cloud and sporadic meteors, Astrophys. J., 743, 129–144, doi:10.1088/0004-637X/743/2/129.

Plane, J. M. C. (2012), Cosmic dust in the earth's atmosphere, Chem. Soc. Rev., 41, 6507-6518, doi:10.1039/C2CS35132C.

Plane, J. M. C., J. D. Carrillo-Sánchez, T. P. Mangan, M. M. J. Crismani, N. M. Schneider, and A. Määttänen (2018), Meteoric Metal Chemistry in the Martian Atmosphere, J. Geophys. Res. – Planets, 123, 695-707, doi:10.1002/2017JE005510.

Plane, J. M. C., W. Feng, and E. C. M. Dawkins (2015), The Mesosphere and Metals: Chemistry and Changes, Chem. Rev., 115(10), 4497-4541, doi:10.1021/cr500501m.

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