2019年09月24日:火星解冻的沙丘-（Sand Dunes Thawing on Mars）

2019年09月24日:火星解冻的沙丘-（Sand Dunes Thawing on Mars）--原图下载

Image Credit & License: ESA, Roscosmos,CaSSIS
说明: 火星上这些奇特的形状是什么？是正在解冻的沙丘。随着春天降临火星的北半球，上面这片由欧洲航天局．火星微量气体任务卫星，在今天5月底拍摄的近北极沙丘，就开始解冻。在稀薄的大气环境中，乾冰(冻结的二氧化碳)和水冰直接昇华成气体。冰较薄的区域，通常先解冻，而曝露出的沙，因为色泽较深，在阳光中吸热较快，更加速冰消融的速率。解冻的过程中，甚至可能出现穿破薄冰的沙喷流。当夏天来临时，融解区将扩及整片沙丘。火星的北极周围环绕着许多类似的新月形沙丘，它们奇特平滑的形状，是受到永不停歇的火星风之雕塑。（ExoMars Trace Gas Orbiter,TGO or ExoMars Orbiter 火星微量气体任务卫星）

原文：

Image Credit & License: ESA, Roscosmos,CaSSIS
Explanation: What are these strange shapes on Mars? Defrosting sand dunes.As Spring dawned on the Northern Hemisphere of Mars, dunes of sand near the pole, as pictured here in late Mayby ESA's ExoMars Trace Gas Orbiter, began to thaw. The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas. Thinner regions of ice typically defrost first revealing sand whose darkness soaks in sunlight and accelerates the thaw. The process might even involve sandy jets exploding through the thinning ice. By Summer, spots will expand to encompass the entire dunes. The Martian North Pole is ringed by many similar fields of barchan sand dunes, whose strange, smooth arcs are shaped by persistent Martian winds.