报告摘要：

The recent approach of comet 67P/Churyumov-Gerasimenko by the spacecraft Rosetta has revealed the presence of astonishing dune-like patterns. How can the radial outgassing, caused by heating when passing close to the sun, produce a vapour flow along the surface of the comet dense enough to transport grains? We show that the vapour flow emitted by the comet around its perihelion spreads laterally in thermal winds, due to the strong pressure difference between zones illuminated by sunlight and those in shadow. Drawing on the physical mechanisms at work for the formation of dunes on Earth and planetary bodies, we can explain the emergence of these bedforms in such extreme cometary conditions at the observed crest-to-crest size, about 10 m. Although generated by a rarefied atmosphere, they are in fact analogous to ripples emerging on granular beds submitted to viscous shear flows.

报告人简介：

Dr. Pan JIA is currently a LabEx PALM Research Fellow at Laboratoire de Physique des Solides (LPS, UMR8502), Université Paris-Sud, Orsay, France. He received his PhD in physics in 2016, under supervision of Profs. Bruno Andreotti and Philippe Claudin 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 and soft matter: patterns and instabilities at interfaces; 2) grains - flow interactions: sediment transport, particle-tracking algorithms, flow visualisations.

References:

P. Jia, B. Andreotti and P. Claudin, Proc. Natl. Acad. Sci. USA 114, pp 2509-2514 (2017).