22-EPN3-099: Formation of Impact Ripples Induced by Different Flow Rates Under Martian Pressure and Temperature
Visit by Aurore Collet and Sabrina Carpy of the Laboratoire de Planétologie et Géosciences (France), to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 22 May – 2 June 2023
Report summary: The conditions for the formation of aeolian ripples depend on the surface characteristics (particle flux, surface roughness, nature of the substrate) and the atmosphere (pressure, temperature, viscosity). The understanding of their formation mechanisms is a real challenge to characterise the interaction between the atmosphere and the substrate of different planetary bodies. Constraining the mechanisms would also allow to go back to past information as on Mars where the atmosphere was not as tenuous as today (Mischna, Lee, et Richardson 2012). A method to link their morphological characteristics (wavelength, amplitude) to the physical characteristics (pressure, temperature, viscosity, particle flux) and verify the associated flow regime (transition, equilibrium) (Selmani et al. 2018) is to use scaling law.
There is currently a significant lack of experimental data to understand the influence of the different physical parameters on the initial formation mechanism and the development of the ripples. On Mars, the formation of ripples under a tenuous atmosphere is still poorly constrained, despite that recent works have attempted to tackle this question (Lapotre et al. 2016; Sullivan et al. 2020). The study of the variation of the flow velocity on a given material (silica sand), can be experimented in a wind tunnel under a Martian atmosphere to understand the formation and the development of the aeolian ripples. A pioneer study in the Martian Chamber formed aeolian ripples with a quartz grain size of 125 μm (Andreotti et al. 2021) but natural ripples generally have a distributed grain size as on Mars where aeolian ripples of centimeter-scale wavelength have been detected on an active dune, with a grain size range of 45 – 500 μm (Ehlmann et al. 2017). Moreover, numerical modelling indicates a link between ripple wavelength, grain flow and the erosion rate of the system (Lester et al. 2022). The interaction between flow velocity, wavelength and erosion rate can be studied in space and time using photogrammetry.
