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This is Scientific American's 60-Second Science. I'm Christopher Intagliata. Got a minute?

Galileo first spotted¹ Saturn²'s rings 400 years ago. But since then, scientists have been stumped³ about how they got there. Because the rings are almost pure water ice—and material in the outer solar system is generally an ice-rock mix. But a new analysis in the journal Nature may have solved the mystery.

Today, Saturn's only massive moon is Titan. But Saturn's fellow gas giant planet Jupiter has four big moons. So Saturn might once have had more—one of which could have had a rocky core surrounded by a shell of water ice. That moon would have interacted with a disk of gas surrounding Saturn at the time, dragging its orbit closer and closer.

As the moon spiraled in, tidal forces would have flexed⁴ its icy shell, stripping off chunks⁵ to build rings a thousand times more massive than Saturn has today. Eventually, ice boulders⁶ in the rings would have smashed into each other, spreading out the rings, and causing the outer edge to spawn⁷ icy moons—the small ones we find orbiting Saturn today.

As for that ancient moon's rocky core? Saturn probably swallowed it up. Leaving Titan unique. And leaving scientists with a puzzle they finally may have solved.

Thanks for the minute. For Scientific American's 60-Second Science, I'm Christopher Intagliata.

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1 spotted
adj.有斑点的，斑纹的，弄污了的
参考例句：
The milkman selected the spotted cows,from among a herd of two hundred.牛奶商从一群200头牛中选出有斑点的牛。 Sam's shop stocks short spotted socks.山姆的商店屯积了有斑点的短袜。

2 Saturn
n.农神，土星
参考例句：
Astronomers used to ask why only Saturn has rings.天文学家们过去一直感到奇怪，为什么只有土星有光环。 These comparisons suggested that Saturn is made of lighter materials.这些比较告诉我们，土星由较轻的物质构成。

3 stumped
僵直地行走，跺步行走( stump的过去式和过去分词 )；把（某人）难住；使为难；（选举前）在某一地区作政治性巡回演说
参考例句：
Jack huffed himself up and stumped out of the room. 杰克气喘吁吁地干完活，然后很艰难地走出房间。 He was stumped by the questions and remained tongue-tied for a good while. 他被问得张口结舌，半天说不出话来。

4 flexed
adj.[医]曲折的，屈曲v.屈曲( flex的过去式和过去分词 )；弯曲；（为准备大干而）显示实力；摩拳擦掌
参考例句：
He stretched and flexed his knees to relax himself. 他伸屈膝关节使自己放松一下。来自辞典例句 He flexed his long stringy muscles manfully. 他孔武有力地弯起膀子，显露出细长条的肌肉。来自辞典例句

5 chunks
厚厚的一块( chunk的名词复数 )；（某物）相当大的数量或部分
参考例句：
a tin of pineapple chunks 一罐菠萝块 Those chunks of meat are rather large—could you chop them up a bIt'smaller? 这些肉块相当大，还能再切小一点吗？

6 boulders
n.卵石( boulder的名词复数 )；巨砾；（受水或天气侵蚀而成的）巨石；漂砾
参考例句：
Seals basked on boulders in a flat calm. 海面风平浪静，海豹在巨石上晒太阳。来自《简明英汉词典》 The river takes a headlong plunge into a maelstrom of rocks and boulders. 河水急流而下，入一个漂砾的漩涡中。来自《简明英汉词典》

7 spawn
n.卵，产物，后代，结果；vt.产卵，种菌丝于，产生，造成；vi.产卵，大量生产
参考例句：
The fish were madly pushing their way upstream to spawn.鱼群为产卵而疯狂地向上游挤进。 These fish will lay spawn in about one month from now.这些鱼大约一个月内会产卵。