图片版权 Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

火星什么时候看起来像是液体呢？即使有液体出现在火星也会因为火星稀薄的大气而蒸发或者结冰，但是持久的大风使火星上的巨大沙丘想液体一样流动。可以从上边的图片中看到当时间才能从春季到夏季时南部有两个平台山，两平台山上的光亮也能从很远处看到。当风从右向左吹的时候，流沙将会从平台周围留下来形成一环一环的花纹。图片里弯曲弧形还带有阴影的沙丘被称为新月形沙丘，而且这些沙丘和火星在太阳系中的孪生兄弟地球上的沙丘类型很相似。新月形沙丘可以在风中保持原形的移动，甚至可以2个沙丘互相穿过而不扰乱对方的形状。每当季节变换的时候，火星上的风可以踢开沙子并且可能作为监测火星上著名风暴的向导。

When does Mars act like a liquid? Although liquids freeze and evaporate quickly into the thin atmosphere of Mars, persistent winds may make large sand dunes appear to flow and even drip like a liquid. Visible on the above image right are two flat top mesas in southern Mars when the season was changing from Spring to Summer. A light dome topped hill is also visible on the far left of the image. As winds blow from right to left, flowing sand on and around the hills leaves picturesque streaks. The dark arc-shaped droplets of fine sand are called barchans, and are the interplanetary cousins of similar Earth-based sand forms. Barchans can move intact a downwind and can even appear to pass through each other. When seasons change, winds on Mars can kick up dust and are monitored to see if they escalate into another of Mars’ famous planet-scale sand storms.

英文原文版权由NASA所有

via APOD

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)&西利天文社