Dusty streaks on the Moon: fingerprints of multiphase flow instabilities

From the crewed Apollo missions to the recent Chinese Chang’e landings, the interaction between spacecraft exhaust plumes and lunar soil produces dusty clouds with high-speed particle ejection. Despite varying landing sites, remarkably stable streak patterns were observed, raising questions about their origin. We solved this puzzle by showing that these patterns were driven by Görtler instability from the curved compressed shear layer of the supersonic but surprisingly laminar jet. This instability creates vortical structures that entrain and eject particles. The number of streaks exhibits an interesting scaling with the jet pressure ratio, which can be modeled with linear instability theory and shows excellent agreement with scaled-down experiments, simulations, and actual observations in landing videos. Our findings provide a fluid physics explanation of extraterrestrial landings, highlighting the role of particle-laden flows and paving the way for future missions to optimize landing strategies and mitigate dust cloud effects on equipment and visibility.