土星的土卫八：有着奇怪表面的卫星
(原标题: Saturn's Iapetus: Moon with a Strange Surface)
2023-02-26
浏览次数: 22
什么会让月亮看起来像核桃？在这张特色图片的底部，可以看到环绕土星卫星土卫八赤道的一个奇怪的山脊，使它看起来像一种流行的可食用坚果。然而，山脊的起源仍然未知，假说包括从下面涌出的冰，从上面坠落的环，以及大约1亿年前形成时留下的结构。同样奇怪的是，土卫八大约有一半是如此黑暗，以至于从地球上看几乎可以消失，而其余的部分则是相当明亮的。观测表明，该地形的黑暗程度出奇地均匀，就好像一层黑暗的涂层最近以某种方式涂在了一个古老的、布满陨石坑的表面上。最后，土卫八周围有几个大的撞击盆地，在图像中心附近可以看到一个400公里宽的陨石坑，周围是陡峭的悬崖。这张特色图片是由绕土星运行的卡西尼号宇宙飞船在2004年底飞越土卫八时拍摄的。
查看原文解释
What would make a moon look like a walnut? A strange ridge that circles Saturn's moon Iapetus's equator, visible near the bottom of the featured image, makes it appear similar to a popular edible nut. The origin of the ridge remains unknown, though, with hypotheses including ice that welled up from below, a ring that crashed down from above, and structure left over from its formation perhaps 100 million years ago. Also strange is that about half of Iapetus is so dark that it can nearly disappear when viewed from Earth, while the rest is, reflectively, quite bright. Observations show that the degree of darkness of the terrain is strangely uniform, as if a dark coating was somehow recently applied to an ancient and highly cratered surface. Last, several large impact basins occur around Iapetus, with a 400-kilometer wide crater visible near the image center, surrounded by deep cliffs that drop sharply to the crater floor. The featured image was taken by the Saturn-orbiting Cassini spacecraft during a flyby of Iapetus at the end of 2004.