现在的北美大陆和欧洲大陆大约在40亿年前是连接在一起的，在那时，加勒多尼亚山脉与现代的喜马拉雅山脉一样雄伟。
About 400 million years ago, when the present-day continents of North America and Europe were joined, the Caledonian mountain chain was the same size as the modern Himalayas.
它大约和木星一样大，但是却是木星质量的20倍，这使它有铅密度的两倍。
It is about the size of Jupiter, but 20 times that planet's mass, making it about twice as dense as lead.
木卫一和木卫二大约和月球一样大，而木卫三和木卫四大概是月球直径的一半。
Io and Europa are about the same size as our moon, whereas Ganymede and Callisto have diameters that are half again our moon's diameter.
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