有发>信封封面怎么写托福阅读真题第293篇
金星、地球和火星都被认为是由相似的材料形成的。它们的铁核占据了行星相似的部分，它们的硅酸盐地幔——地幔是行星中心核和外地壳之间的物质层——熔化产生相似种类的火山岩。相比之下，水星是四颗内行星或类地行星中最小且距离太阳最近的行星，它可能是由不同的整体成分形成的，或者可能是在与其他类地行星不同的条件下形成的。这颗行星有一个巨大的铁核，这表明这颗行星的铁含量至少是其他类地行星的两倍，或者几乎所有来自整体成分的铁都被拉入了它的核心，使得它的地幔几乎不含铁。同时，这颗行星最近没有火山活动，因此，与金星、地球和火星不同，它的内部可以假定为静止的。缺乏火山活动通常被认为意味着地球已经基本失去了内部热量。然而，水星有一个小磁场。磁场通常被认为是由热损失引起的地幔中的流体运动引起的。不知何故，水星创造了一种平衡，可以在没有地幔运动的情况下产生磁场。
水星的平均密度为每立方英尺 341 磅，仅低于密度最大的行星地球的每立方英尺 347 磅。这颗行星的高密度最初是通过测量水手号任务在水星异常强大的重力场控制下向水星的惊人加速度而发现的。地球是一颗更大的行星，因此它的内部压力要高得多，将物质压成密度更大
的形式。除去压力的影响，水星的密度实际上比地球高得多，因此它是太阳系中密度最大的行星。这颗行星的高密度被认为意味着它含有大量的铁——按比例来说，比任何其他行星都多。Lorn 是太阳系内最常见的致密元素，它很可能是造成水星高密度的原因。如果水星的额外密度是由于铁含量，那么水星的核心质量占 60% 或更多，这是太阳系中任何行星的行星半径最大的核心。水星的核心半径可能在 1,120 到 1,180 英里之间，接近水星直径的 75%。日至少是金星、地球或火星金属含量的两倍。
urrent models for planetary formation suggest that any terrestrial planet should form with a large percentage of silicates, which would make up a thick mantle above the core, as they do on Venus, Earth, and Mars. Mercury may have lost most of its silicate mantle in some catastrophic event after its early formation. The simplest candidate for this event is a giant impact. If a large body struck Mercury more or less directly, then its iron would combine with Mercury's into an unusually large core, and much of Mercury's silicate mantle could have been lost to space. The impacting body may also have been made predominantly of metal, like an iron meteorite. In this scenario, the metal meteorite would combine with the early, small pro to Mercury, creating a planet with an unusually large iro
n core. lternatively, the silicate mantle could have been removed by vaporization in a burst of heat from the early Sun. third possibility is that there may have been strong compositional variation in the early solar system and that in fact Mercury formed with the iron-rich composition it now ems to posss. Finally, Mercury could have differentiated in a particularly oxygen-poor environment. Without oxygen, iron will preferentially form a metal and sink into the core rather than forming iron oxide and combining into silicate mantle materials. In this scenario, Mercury could have started with the same bulk composition and ended with its current structure without having endured a giant impact.
1.Venus, Earth, and Mars are all thought to have formed from similar materials. Their iron cores take up similar fractions of the planets, and their silicate mantles- -the mantle is the layer of material between a planet's central core and its outer crust- -melt to produce similar kinds of volcanic rocks. y contrast, Mercury, the smallest and clost to the Sun of the four inner, or terrestrial, planets, may have been formed from a different bulk composition, or it may have formed under different conditions than the other terrestrial planets. The planet has a huge iron core, indicating either that the planet contains at least 个人简历怎么写
简单小手工twice the iron content of the other terrestrial planets or that virtually all the iron from the bulk composition was pulled into its core, leaving its mantle almost iron-free. t the same time, the planet shows no recent volcanic activity, and so, unlike Venus, Earth, and Mars, its interior can be assumed to be stationary. The lack of volcanic activity is usually taken to mean that the planet has largely finished losing its internal heat. Mercury, however, has a small magnetic field. Magnetic fields are generally accepted to be caud by fluid movements in the mantle caud by heat loss. Somehow Mercury has created a balance that allows the generation of a magnetic field in the abnce of mantle movements.
怀孕可以吃薯片吗2.Venus, Earth, and Mars are all thought to have formed from similar materials. Their iron cores take up similar fractions of the planets, and their silicate mantles- -the mantle is the layer of material between a planet's central core and its outer crust- -melt to produce similar kinds of volcanic rocks. y contrast, Mercury, the smallest and clost to the Sun of the four inner, or terrestrial, planets, may have been formed from a different bulk composition, or it may have formed under different conditions than the other terrestrial planets. The planet has a huge iron core, indicating either that the planet contains at least
twice the iron content of the other terrestrial planets or that virtually all the iron from the bulk composition was pulled into its core, leaving its mantle almost iron-free. t the same time, the planet shows no recent volcanic activity, and so, unlike Venus, Earth, and Mars, its interior can be assumed to be stationary. The lack of volcanic activity is usually taken to mean that the planet has largely finished losing its internal heat. Mercury, however, has a small magnetic field. Magnetic fields are generally accepted to be caud by fluid movements in the mantle caud by heat loss. Somehow Mercury has created a balance that allows the generation of a magnetic field in the abnce of mantle movements.
3.表扬的英文Venus, Earth, and Mars are all thought to have formed from similar materials. Their iron cores take up similar fractions of the planets, and their silicate mantles- -the mantle is the layer of material between a planet's central core and its outer crust- -melt to produce similar kinds of volcanic rocks. y contrast, Mercury, the smallest and clost to the Sun of the four inner, or terrestrial, planets, may have been formed from a different bulk composition, or it may have formed under different conditions than the other terrestrial planets. The planet has a huge iron core, indicating either that the planet contains at least
twice the iron content of the other terrestrial planets or that virtually all the iron from the bulk composition was pulled into its core, leaving its mantle almost iron-free. t the same time, the planet shows no recent volcanic activity, and so, unlike Venus, Earth, and Mars, its interior can be assumed to be stationary. The lack of volcanic activity is usually taken to mean that the planet has largely finished losing its internal heat. Mercury, however, has a small magnetic field. Magnetic fields are generally accepted to be caud by fluid movements in the mantle caud by heat loss. Somehow Mercury has created a balance that allows the generation of a magnetic field in the abnce of mantle movements.奥运会的由来
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4.Venus, Earth, and Mars are all thought to have formed from similar materials. Their iron cores take up similar fractions of the planets, and their silicate mantles- -the mantle is the layer of material between a planet's central core and its outer crust- -melt to produce similar kinds of volcanic rocks. y contrast, Mercury, the smallest and clost to the Sun of the four inner, or terrestrial, planets, may have been formed from a different bulk composition, or it may have formed under different conditions than the other terrestrial planets. The planet has a huge iron core, indicating either that the planet contains at least
twice the iron content of the other terrestrial planets or that virtually all the iron from the bulk composition was pulled into its core, leaving its mantle almost iron-free. t the same time, the planet shows no recent volcanic activity, and so, unlike Venus, Earth, and Mars, its interior can be assumed to be stationary. The lack of volcanic activity is usually taken to mean that the planet has largely finished losing its internal heat. Mercury, however, has a small magnetic field. Magnetic fields are generally accepted to be caud by fluid movements in the mantle caud by heat loss. Somehow Mercury has created a balance that allows the generation of a magnetic field in the abnce of mantle movements.
