火星上的大峡谷（图）  

                                      Mars's Grand Canyon

Call it the Super-Grand Canyon. Melas Chasma on Mars is 9 kilometers deep in some places, or nearly six times deeper than Earth's famous landmark on average. How the giant feature was formed, itself one small stretch of the 4000-kilometer-long Valles Marineris rift valley, remains a mystery. But one thing seems evident: water played a role in its history. In this view, one of several images of Melas Chasma released today, a computer has reconstructed 3D images taken with the European Mars Express orbiter's High-Resolution Stereo Camera. Part of the canyon wall collapsed in multiple landslides in the distant past, with debris fanning out into the valley below. Scientists analyzing the texture of the rocks deposited by the landslides say they were transported by liquid water, water ice, or mud. They also see evidence of sediments in the exposed sides of the canyon, and the lighter-colored rocks apparently are composed of sulfates, another strong sign of a wet martian past.

且称之为“超级大峡谷”吧。火星上的米拉斯峡谷有的地段深达9千米，比地球上著名的标志性峡谷平均起来深将近六倍。米拉斯峡谷本身是4000公里长的水手峡谷的一小段，这种巨大的地貌特征是如何形成的仍然是个谜。但是有一件事情是显而易见的：水在大峡谷形成的历史上起到了一定的作用。这张图片是今天发布的有关米拉斯峡谷的数张图片之一，是由欧洲的“火星快车”探测器上搭载的高分辨立体照相机拍摄的，利用一台计算机重现了其3D形象。在遥远的过去发生的多次滑坡中，峡谷的部分谷壁已经崩塌，碎屑散落谷底。科学家们分析了滑坡造成的沉积岩，他们表示，这些沉积岩是由液态水、水冰或烂泥冲过来的。他们在该峡谷暴露出侧面的沉积层中也发现了证据，较为浅色的岩石显然是由硫酸盐类构成的，这是火星过去有水的另外一个有力证据。