火星上的生存机遇（火星上是否有四季）
火星上的生存机遇（火星上是否有四季）The progression begins at left (Panel A) in early spring when the ground is covered by a seasonal layer of carbon dioxide ice (dry ice) about 2 feet thick. As spring progresses the ice cracks (Panel B) releasing dark sand from the dune below. When pressurized gas trapped below the ice layer is released it carries along sand and dust to the top of the ice layer where it is dropped in fan-shaped
NASA/JPL-Caltech/Univ. of Arizona
美国宇航局火星侦察轨道器上的高分辨率成像科学实验 (HiRISE) 相机拍摄了这一系列火星北极地区沙丘的假彩色照片。五个面板中的每一个都覆盖的区域大约为 0.8 英里（1.3 公里）宽。
这一进程从早春的左侧（图A）开始，当时地面被一层约 2 英尺厚的季节性二氧化碳冰（干冰）覆盖。随着春天的到来，冰裂开（图 B），从下面的沙丘中释放出黑色的沙子。当被困在冰层下方的加压气体被释放时，它会将沙子和灰尘带到冰层的顶部，在那里它以扇形沉积物的形式下坡和顺风下降（面板C和D）。随着覆盖的季节性冰层蒸发回大气中，最后一个面板显示了越来越多的黑暗沙丘。
Thawing 'Dry Ice' Drives Groovy Action on MarsThe High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter snapped this series of false-color pictures of sand dunes in the north polar region of Mars. The area covered in each of the five panels is about 0.8 mile (1.3 kilometers) wide.
The progression begins at left (Panel A) in early spring when the ground is covered by a seasonal layer of carbon dioxide ice (dry ice) about 2 feet thick. As spring progresses the ice cracks (Panel B) releasing dark sand from the dune below. When pressurized gas trapped below the ice layer is released it carries along sand and dust to the top of the ice layer where it is dropped in fan-shaped deposits downhill and downwind (panels C and D). The final panel shows more and more of the dark dunes as the overlying layer of seasonal ice evaporates back into the atmosphere.
