It could have come from the impacts of comets, for instance, or from within the Moon.
这些水可能是来自撞击的彗星，或来自月球内部。
This radiation pressure is thought to shape the tails of comets and is useful for pushing solar sails in space.
这种辐射压力被认为是彗尾形成的原因。 另外，它也是太阳帆在太空中前进的动力来源。
The rings—there are thousands—are made up of billions of ice and rock particles, thought to be pieces of comets, asteroids, or shattered moons
这些环，有成千上万个，是由数十亿个冰和岩石的粒子所组成，这些粒子被认为是彗星、小行星和粉碎卫星的碎片。
Their explanation: a faint, far-off companion star to the Sun was sending down a rain of comets when it reached just the right point in its orbit.
他们的解释是这样的：遥远的地方，太阳有一颗微弱的伴星，当它到达轨道的某个定点时，就会产生大量彗星。
Every so often a comet gets flung out of the Oort Cloud, a swarm of comets on the fringes of the solar system, and gets close enough to Earth for us to see it.
经常有彗星被甩出奥尔特云(在太阳系边缘的彗星群)，并靠近地球到肉眼可以观测的距离。
In Earth's formative years, it was hit by thousands of comets like this.
在地球的最初岁月中，它曾被成千上万个这样的彗星撞击。
Edmond Halley, English astronomer and mathematician, renowned for studies of comets, was born in London.
以研究彗星称著的英国天文学家、数学家埃德蒙·哈雷生于伦敦。
Applying the results obtained in this paper to the motion of comets, discuss the nongravitational effect on the orbit of some comets.
文中还将研究结果应用到彗星运动上 ，讨论彗星轨道中非引力效应。
Quite a large number of comets are discovered every century, but most of them are extremely faint objects, far below the limits of the unaided eye.
每一个世纪都发现相当多的彗星，但大多数彗星都是非常微弱的天体，远不能为肉眼所见。
Note: Since astronomers have not fully understood the mechanism account for the brightening of comets, they can only predict by referring to past comets.
注：由于天文学家还未完全掌握彗星增光的机制，因此只能参考过去其他彗星的情况作出预报。
It was learned that in the world of comets, the most famous is Halley's, and one of the four major meteor showers is from Aquarius, with its parent comet Halley's comet.
据介绍，在彗星世界里，最著名的就是哈雷彗星了，四大流星雨之一的宝瓶座流星雨的母体彗星就是哈雷彗星。
The cloud starts from a point about 93 billion miles from the Sun and stretches for around three light years and contains billions of comets, most of them small and hidden.
这个云团从距离太阳930亿英里外的一个点扩展到大约三光年的规模，同时包含了数以亿计的彗星，其中大部分彗星很小，而且是隐藏的。
Most of it is still there, frozen solid in, among other things, the rings of Saturn, Jupiter's moon Europa, the bodies of Neptune and Uranus and billions upon billions of comets.
这些水分至今还以冰冻的形式存在于土星环，木星的卫星欧罗巴，海王星、天王星以及数以十亿计的彗星之中。
We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun.
很多彗星接近太阳时，我们可以用肉眼看见，因为它们的彗发和彗尾可以反射阳光，甚至因为受阳光激发而自发光。
The comet currently headed for the sun may be part of the so-called Kreutz group of comets, which are known for having orbits that bring them within a few hundred thousand miles of the sun.
这颗冲向太阳的彗星可能是所谓的克鲁兹彗星家族的一员，这个彗星家族以其特殊的运行轨道而闻名于世，该轨道会将其带入太阳附近。
The comet currently headed for the sun may be part of the so-called Kreutz group of comets, which are known for having orbits that bring them within a few hundred thousand miles of the sun.
这颗冲向太阳的彗星可能是所谓的克鲁兹彗星家族的一员，这个彗星家族以其特殊的运行轨道而闻名于世，该轨道会将其带入太阳附近。
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