Galileo first ______1_____ Saturn’s rings 400 years ago. But since then, scientists have ______2_____ 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 ______3_____, tidal forces would have flexed its icy shell, stripping off chunks to build rings a thousand times more massive than Saturn has today. Eventually, ice boulders in the rings would have ______4____ each other, spreading out the rings, and causing the outer edge to spawn icy moons—the small ones we find orbiting Saturn today.
As for that ancient moon’s rocky core? Saturn probably _____5_____. Leaving Titan unique. And leaving scientists with a puzzle they finally may have solved.
【視聽版科學(xué)小組榮譽(yù)出品】
spotted been stumped about spiraled in smashed into swallowed it up
土星環(huán)——衛(wèi)星的殘跡 自四百年前土星環(huán)被伽利略首次發(fā)現(xiàn)以來，科學(xué)家一直難以對(duì)其成因做出解釋。因?yàn)橥列黔h(huán)幾乎純粹由水冰構(gòu)成-而外太陽系的物質(zhì)構(gòu)成通常是冰巖混合物。不過，發(fā)表在《自然》雜志上的一項(xiàng)新的分析成果或許可以解開謎團(tuán)。 現(xiàn)如今，土衛(wèi)六是土星的唯一一顆大型衛(wèi)星。而同樣是氣態(tài)行星的木星卻有四顆大衛(wèi)星。所以土星也許曾經(jīng)有過多個(gè)衛(wèi)星-其中一個(gè)可能是由水冰外殼包裹著巖石核心構(gòu)成。當(dāng)時(shí)，這顆衛(wèi)星可能與土星周圍的氣態(tài)圓盤互相作用，將其軌道向土星拉近。 當(dāng)這顆衛(wèi)星做螺旋運(yùn)動(dòng)逐漸接近土星時(shí)，引潮力會(huì)不斷拉伸和壓縮衛(wèi)星的冰狀外殼，將其剝離成塊狀，形成一個(gè)比現(xiàn)在的土星環(huán)還要大一千倍的環(huán)。最終，土星環(huán)中的冰石互相撞擊，四散開來，并在土星環(huán)外緣形成我們現(xiàn)如今發(fā)現(xiàn)繞土星運(yùn)行的小型冰態(tài)衛(wèi)星。 至于那顆古老衛(wèi)星的巖石內(nèi)核呢？大概是土星將它吞噬了。只留下獨(dú)一無二的土衛(wèi)六，并留給科學(xué)家一個(gè)最終可能解開的謎題。