Description
Cosmic dust injects 31 ± 18 t d$^{-1}$ of material into the atmosphere of Venus [Carrillo-Sanchez et al., 2020], which ablates between 105 and 120 km. The ablated metals produce neutral and ionized metal layers. On Earth (receiving 28 ± 16 t d$^{-1}$ of cosmic dust) these layers have been detected by ground-based lidar, rocket-borne mass spectrometry and space-based spectroscopy, but they have yet to be observed on Venus.
In this study, the diurnal and latitudinal variability of the Na, Mg and Fe layers was modelled to explore the feasibility of their spectroscopic detection. We used the Venus Planetary Climate Model with a Meteoric Input Function developed for Venus (Carrillo-Sanchez et al., 2020), and detailed neutral and ion-molecule chemistry for Na, Fe and Mg.
The metal layers exhibit pronounced diurnal variability, peaking in concentration on the nightside before the morning terminator. The latitudinal variability is strongly linked to the zonal and meridional wind circulation. Because the Na and Mg layers peak 10 km higher than the Fe layer, Na and Mg tend to be concentrated in the northern hemisphere, and Fe in the southern hemisphere.
These results indicate the Na layer on Venus should be detectable from a terrestrial telescope observing solar-pumped resonance fluorescence at 589 nm, particularly around the morning terminator in the northern hemisphere. We highlight the importance of observing metal layers in the CO$_2$-rich atmosphere of Venus as a contrast with the O$_2$–rich terrestrial atmosphere, in order to exploit the growing collection of Na observations around exoplanets.
