APOD090420：火星上的流动沙丘
http://apod.nasa.gov/apod/astropix.html2009 April 20
Flowing Barchan Sand Dunes on Mars
http://apod.nasa.gov/apod/image/0904/sandmars_mro.jpg
Credit: HiRISE,MRO,LPL (U. Arizona),NASA
Explanation:
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, where the season is 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 downwind and can even appear to pass through each other.Over the past few weeks, winds on southern Mars have been kicking up dust and are being watched to see if they escalate into another of Mars' famous planet-scale sand storms. 今天的北京天文馆的翻译比较快
http://www.bjp.org.cn/apod/today.htm
火星上流动的弧形沙丘
影像提供：HiRISE, MRO, LPL (U. Arizona), NASA
说明：
什么时候火星表面变得像液体一样？尽管火星上的液体凝结并很快地蒸发到稀薄的大气中，但是如今的风使得火星表面形成巨大的流动沙丘，看起来就像落下的水滴一样。可以看到上面影像右侧是两座位于火星南部的平顶山，而那里的季节正从春天向夏天转变。在影像的左侧还可以看到另一座发亮的圆顶山丘。当风从右向左吹时，流动的沙子和周围的丘陵形成了独特的纹理。暗色的弧状细沙堆被称为弧形沙丘，这与地球上沙丘形成类似。弧形沙丘能顺着风向完整地移动，有时甚至能相互通过。过去的几周里，在火星南部，风早已扬起了沙尘，如果情况慢慢变糟，很可能会形成火星另一种著名的全球性气候--沙尘暴，让我们拭目以待。 本帖最后由 gohomeman1 于 2009-4-20 21:08 编辑
APOD的大图,2037X2532。
http://apod.nasa.gov/apod/image/0904/sandmars_mro_big.jpg 左边那个亮区不是说是个外星人的脸吗？据说还有神殿、建筑什么的，完全就一个SC中的失落的神殿啊！ 两个白色突起的小东西是什么？？ 一座发亮的圆顶山丘
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