在彗星里，它可算是个庞然大物。
这颗彗星的轨道和地球的轨道相交。
我们不太确定这颗彗星是否会错过地球。
We were not altogether sure that the comet would miss the Earth.
这颗彗星将于2061年返回，到时我们都可以看到它。哦，无论如何，我们子孙是可以看到的。
The comet is going to come back in 2061 and we are all going to be able to see it. Well, our offspring are, anyway.
彗星在组成上与气态巨行星相似。
我迫不及待地想看到那颗新的彗星。
彗星与地球大约同时形成。
Comets were formed around the same time the Earth was formed.
这些冰和小岩石粒的松散集合形成了彗星。
Loose collections of these ices and small rocky particles form into comets.
这种周期性轨道只是彗星生命中的一个阶段。
This kind of periodic orbit is only a phase in a comet's life.
当彗星接近太阳时，其中的一些气体开始解冻。
As a comet gets closer to the sun, some gases in it begin to unfreeze.
在很大程度上，Roids只是小行星和彗星的小碎片。
Roids are, for the most part anyway, they are just smaller bits of asteroids and comets.
那么讲到流星体从何而来，我们就需要讨论下彗星和小行星。
So to talk about where meteorites come from, we need to talk about comets and asteroids.
它们与来自彗星的尘埃颗粒结合在一起，形成了巨大的云团。
They combine with dust particles from the comet to form a huge cloud.
太阳系也有两类类似的物体，比行星还小——即小行星和彗星。
The solar system also has two analogous classes of objects, smaller than planets—namely, asteroids and comets.
现在我们继续讨论，谈谈轨道，特别是那些所谓的周期轨道彗星。
Let's continue our discussion now by talking about orbits, especially those of the so-called periodic-orbit comets.
当彗星靠近太阳时，它的冰层融化，释放的气体和尘埃飘向太空。
As the comet nears the sun, its ice melts, releasing gas and dust that stream away into space.
我们认为，撞击月球的流星或经过的彗星尾巴可能会留下一些水分子。
We think meteors that crashed into the moon or tails of passing comets may have introduced water molecules.
抱着埃伦在月光中飞翔，他们像彗星一样射入永恒，客厅里的钟停了。
Soaring through the moonlight with Ellen in his arms, the pair of them shooting like comets into eternity while the clock in the parlor stops.
其次，木星的巨大质量阻止了大多数与太阳结合的彗星穿透太阳系内部。
Second, Jupiter's enormous mass prevents most Sun-bound comets from penetrating the inner solar system.
只要有足够时间，跟彗星一样的行星最终会完全蒸发掉，但那大约需要一万亿年。
Given enough time, the comet-like planet could theoretically evaporate away completely, but it would take about a trillion years.
彗星在圆形轨道上形成，但当它们冒险太接近行星时，就会被引力抛入现在的椭圆轨道。
Comets formed in circular orbits but were gravitationally flung into their present-day elliptical orbits when they ventured too close to planets.
我现在不打算深入讨论彗星和小行星了，但是我们稍后会再回到这个点上，讨论这方面的内容。
I'm not going to go into any depth on comets and asteroids now, but we'll come back later and do that.
“菲莱”号从地球出发的旅行已经花了十年的时间！科学家们不知道彗星的表面会是什么样子。
The trip from Earth by "Philae" had taken ten years! The scientists had no idea what the surface of the comet would be like.
在任何一年中，大约有十几颗已知的彗星在其轨道中接近太阳。当然，一般人看不到所有的彗星。
In any given year, about a dozen known comets come close to the sun in their orbits, the average person can't see them all, of course.
太阳是一个巨大的旋转系统的中心，这个旋转系统由九大行星、它们的卫星和无数的小天体组成，包括小行星、彗星和流星体。
The Sun is the hub of a huge rotating system consisting of nine planets, their satellites, and numerous small bodies, including asteroids, comets, and meteoroids.
尽管如此，天文学家们仍然相信，当一颗彗星接近太阳时——这是他们可以研究它的地方——太阳的高温将会移除损坏的表层，露出内部。
Nevertheless, astronomers still believed that when a comet approached the Sun—where they could study it—the Sun's intense heat would remove the corrupted surface layer, exposing the interior.
然而，大约在同一时间，科学家们意识到彗星可能含有衰变的放射性同位素，这些同位素可能使彗星内部的温度升高到导致内部进化的温度。
About the same time, though, scientists realized comets might contain decaying radioactive isotopes that could have warmed cometary interiors to temperatures that caused the interiors to evolve.
哈雷彗星将在2061年返回。
通常，一年只有一到两颗彗星明亮得肉眼可见。
Usually there is only one or two a year bright enough to be seen with the naked eye.
1995年发现的海尔-波普彗星是一颗异常明亮的彗星。
Comet Hale-Bopp, discovered in 1995 was an unusually bright comet.
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