2025年9月1日
Callisto: Dirty Battered Iceball
Image Credit: NASA, JPL-Caltech, Voyager 2; Processing & License: Kevin M. Gill;
Explanation: Its surface is the most densely cratered in the Solar System — but what’s inside? Jupiter‘s moon Callisto is a battered ball of dirty ice that is larger than the planet Mercury. It was visited by NASA’s Galileo spacecraft in the 1990s and 2000s, but the recently reprocessed featured image is from a flyby of NASA’s Voyager 2 in 1979. The moon would appear darker if it weren’t for the tapestry of light-colored fractured surface ice created by eons of impacts. The interior of Callisto is potentially even more interesting because therein might lie an internal layer of liquid water. This potential underground sea is a candidate to harbor life — similar with sister moons Europa and Ganymede. Callisto is slightly larger than Luna, Earth’s Moon, but because of its high ice content is slightly less massive. ESA’s JUICE and NASA’s Europa Clipper missions are now headed out to Jupiter to better investigate its largest moons.
Tomorrow’s picture: flaming sky horse
卡利斯多: 肮脏且满是伤痕的冰球
影像提供: NASA, JPL-Caltech, Voyager 2; 影像处理与授权: Kevin M. Gill;
说明: 它的表面是太阳系中陨石坑最密集的地方-但是它的内部是什么样子呢？木星的卫星卡利斯多（木卫四）是一颗受损的脏冰球，其体积比行星水星还大。美国国家航空航天局NASA的伽利略号探测器在1990年代和2000年代曾拜访过它，但最近重新处理的主题影像是来自1979年NASA的旅行者2号飞掠时所拍摄。如果不是因为数亿年撞击形成的浅色破碎表面冰层，这颗卫星看起来会显得更暗。卡利斯多的内部可能更有趣，因为其中可能存在一层液态水。这个潜在的地下海洋可能是孕育生命的候选地，类似于其姊妹卫星欧罗巴（木卫二）和甘尼米德（木卫三）。卡利斯多比月球，也就是地球的月亮稍大，但由于其高冰含量，质量也稍小。欧洲空间局的JUICE和NASA的欧罗巴快船任务现在正前往木星，以更好地研究其最大的卫星。
明日的图片: flaming sky horse
