报告题目：Rippled patterns induced by hydrodynamic instabilities in planetary environment
Rippled patterns were observed in planetary environment by the recent approaches on comet 67P and Pluto. An explanation is proposed for the giant granular ripples observed by spacecraft Rosetta at the surface of the comet 67P. We show that the outgassing flow across a porous surface granular layer and the strong pressure gradient associated with the day-night alternance are responsible for thermal superficial winds. We show that these unexpected patterns are analogous to ripples emerging on granular beds submitted to viscous shear flows. Also, we propose a model for rhythmic, dune-like patterns observed on Sputnik Planum of Pluto. Their emergence and evolution are related to the differential condensation/sublimation of nitrogen ice. We show that the temperature and pressure in Pluto’s atmosphere are almost homogeneous and steady, and that heat flux from the atmosphere due to convection and turbulent mixing is responsible for the emergence of these sublimation patterns, in contrast to the penitentes instability due to solar radiation.
Pan JIA received his PhD in physics in 2016 at Laboratoire de Physique et Mécanique des Milieux Hétérogènes (PMMH) in École Supérieure de Physique et de Chimie Industrielles (ESPCI), Paris, France. His research interests include 1) physics/mechanics of fluids: thermo-hydrodynamic instabilities at interfaces; 2) grains-flow interactions: sediment transport, particle-tracking algorithms, flow visualisations.