土星的土卫八：彩绘卫星
(原标题: Saturn's Iapetus: Painted Moon)
2026-07-05
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土星的卫星土卫八发生了什么？这个奇怪的世界的大部分地方像煤一样黑暗，而另一些地方像雪一样明亮。为了更好地了解这颗颜色不同寻常的卫星，2007年，美国国家航空航天局（NASA）指示当时绕土星运行的卡西尼号（Cassini）宇宙飞船飞入土星2000公里以内。这张照片是从大约75000公里外拍摄的，是土卫八总是尾随的半球。在南部看到的一个巨大的撞击坑跨度500公里，似乎重叠在一个类似大小的旧陨石坑上。深色物质越来越多地覆盖在土卫八的最东端，使陨石坑和高地都变暗。一个主要的假设是，深色物质主要是相对温暖但肮脏的冰升华时留下的富含碳的土壤的一种形式。这种深色物质的最初涂层可能是由来自其他卫星的流星释放的碎片堆积而成的。拼图月亮：每日天文拼图
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What has happened to Saturn's moon Iapetus? Vast sections of this strange world are dark as coal, while others are as bright as snow. To help better understand this unusually tinted moon, in 2007 NASA directed the robotic Cassini spacecraft then orbiting Saturn to swoop within 2,000 kilometers. Pictured here, from about 75,000 kilometers out, is the hemisphere of Iapetus that is always trailing. A large impact crater seen in the south spans 500 kilometers and appears superposed on an older crater of similar size. The dark material is seen increasingly coating the easternmost part of Iapetus, darkening craters and highlands alike. A leading hypothesis is that the dark material is mostly a form of carbon-rich soil leftover from when relatively warm but dirty ice sublimates. An initial coating of this dark material may have been effectively painted on by the accretion of meteor-liberated debris from other moons. Jigsaw Moon: Astronomy Puzzle of the Day