[揽瓜阁精读] 219.月球形成的三种理论

Peggy一定行

•        Astronomers developed three different hypotheses for the origin of Earth’s moon
•        The fission hypothesis: the moon formed by the fission of Earth
o        Young Earth spun fast enough---潮汐将地球分成两半
o        地球分化以后，月亮由地壳物质形成
o        Problems: no one knows+ where+ the moon’s orbit is not in the plane of Earth’s equator月球的轨道不在地球赤道的平面上
•        The condensation hypothesis: 地球和月球是从同样的云层物质中凝结而成的
o        Problems: no same chemical composition and density
o        Moon：poor in heavy elements and in volatiles+ same rations of oxygen isotopes
•        The capture hypothesis: the moon formed somewhere else and later captured by Earth
o        如果月球从水星轨道内形成，热度会阻碍固体金属颗粒形成，只有高熔点金属氧化物才能凝结成固体
o        Mercury kicked the moon out of Earth
o        Problems: require highly unlikely events: interactions with Mercury and Earth---require a chain of unlikely coincidences
•        1970s: develop a new theory---combine fission and capture
•        The large-impact theory: moon formed from debris ejected into a disk around Earth by the impact of a large body地球周围一个大星体的撞击把碎片喷射进星团，形成了月球
o        Twice as large as Mars
o        Earth and moon---collision and merger of two very large planetesimals 星子
o        Large body---Earth ejected debris---moon撞击熔化原始地球，掉落物质最够热熔化形成月球。
o        Fit well with the evidence

Fission n. 裂变；分裂；分体；分裂生殖法
Spun (spin) v. （使）快速旋转；（使）急转身
Angular momentum 角动量
Equator n. 赤道
Condensation n. 冷凝，凝结
Volatile adj. 挥发性，易挥发的，易失的 n. 挥发物
Mercury n. 水星
Solid metallic grains 固体金属晶粒
Coincidence n. 巧合，同时发生；相符，一致；符合
Rip v.（使）撕裂，（使）划破；迅速扯开，猛力去除；（迅速）贯穿，穿过；划出（孔洞），击穿；抢掠，剥夺；严厉批评，训斥；利用程序将（光盘上的音序）复制到硬盘驱动器上
Magma 岩浆

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