火星的暗沙流瀑

2025年6月29日

Dark Sand Cascades on Mars
Image Credit: NASA, HiRISE, MRO, LPL (U. Arizona)

Explanation: Are these trees growing on Mars? No. Groups of dark brown streaks have been photographed by the Mars Reconnaissance Orbiter on melting pinkish sand dunes covered with light frost. The featured image was taken in 2008 April near the North Pole of Mars. At that time, dark sand on the interior of Martian sand dunes became more and more visible as the spring Sun melted the lighter carbon dioxide ice. When occurring near the top of a dune, dark sand may cascade down the dune leaving dark surface streaks — streaks that might appear at first to be trees standing in front of the lighter regions but cast no shadows. Objects about 25 centimeters across are resolved on this image spanning about one kilometer. Close ups of some parts of this image show billowing plumes indicating that the sand slides were occurring even while the image was being taken.

Celestial Surprise: What picture did APOD feature on your birthday? (post 1995)
Tomorrow’s picture: raining stars

火星的暗沙流瀑
影像提供: NASA, HiRISE, MRO, LPL (U. Arizona)

说明: 这些是火星上的树木吗？不是。这些由火星勘测轨道飞行器摄于2008年4月的暗棕色条纹，出现在火星北极区、上头覆盖着消融中淡色薄霜的粉红沙丘上。拍摄这幅主题影像时，随着火星春阳消融淡色的干冰，位于火星沙丘内的暗沙逐渐曝露出来。而位在丘顶的暗沙，有时会流泄下边坡，形成这种暗色的表面流迹，而且在较淡色的表面衬托之下，乍看酷似树林，只是缺少影子。这幅涵盖了1公里宽区域的影像，可解析出跨幅25公分以上的结构。放大检视部份的区域，可见到飞扬的羽状烟尘，显示在拍照时，正有细沙流泄而下。