As comets go, it is a whopper.
在彗星里，它可算是个庞然大物。
Comets are similar in composition to the gas giants.
彗星在组成上与气态巨行星相似。
Loose collections of these ices and small rocky particles form into comets.
这些冰和小岩石粒的松散集合形成了彗星。
So to talk about where meteorites come from, we need to talk about comets and asteroids.
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。
Roids are, for the most part anyway, they are just smaller bits of asteroids and comets.
在很大程度上，Roids只是小行星和彗星的小碎片。
I'm not going to go into any depth on comets and asteroids now, but we'll come back later and do that.
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。
Second, Jupiter's enormous mass prevents most Sun-bound comets from penetrating the inner solar system.
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。
We think meteors that crashed into the moon or tails of passing comets may have introduced water molecules.
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。
The solar system also has two analogous classes of objects, smaller than planets—namely, asteroids and comets.
太阳系也有两类类似的物体，比行星还小——即小行星和彗星。
Let's continue our discussion now by talking about orbits, especially those of the so-called periodic-orbit 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。
Comets formed in circular orbits but were gravitationally flung into their present-day elliptical orbits when they ventured too close to planets.
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。
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.
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。
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.
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。
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.
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。
Explore an asteroids and comets interactive.
探索一颗小行星和彗星们的相互作用。
A number of recent missions have ventured to comets.
最近的许多太空任务与彗星有关。
Lulin, like all comets, isa clump of frozen gases mixed with dust.
鹿林彗星和其他彗星一样，是一堆冰气体和尘埃组成。
Comets are often known as dirty snowballs, and consist mainly of ice and rock.
彗星一般被认为是一些脏雪球，主要由冰和岩石构成。
The nuclei of most comets are thought to measure 10 miles (16 km) or less.
大部分彗星的彗核估计有10英里（16公里）宽。
Stars would stay fixed, but objects like comets, asteroids, and planets moved.
通过这种方法可以观察到，恒星是固定不动的，而像彗星、小行星和行星这样的物体都在移动。
Comets, by contrast, are relatively pristine - at least, below their outer crust.
相比之下，彗星则相对原始——至少在它们的外壳之下是原始的。
An unseen companion star, nicknamed "Nemesis," may be sending comets towards Earth.
一颗看不见的伴星，绰号“复仇者(Nemesis)，可能会导致彗星撞击地球。”
Comets leave a trail of debris behind them that can lead to meteor showers on Earth.
彗星会在经过的地方留下一些碎片，这些碎片可以引起地球上的流星雨现象。
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。
The orbits comets take sometimes end with them colliding with planets and their moons.
一些在轨彗星有时会以与行星或其卫星发生碰撞的形式走向终结。
Comets lose ice and dust each time they come near the sun, leaving behind trails of debris.
彗星每次接近太阳时，都会将一部分冰和尘埃遗留在彗尾的遗迹中。
Until now, it was thought that comets were the only objects that still slammed into Jupiter.
直到现在，人们都认为彗星是唯一一个还撞击木星的天体。
Until now, it was thought that comets were the only objects that still slammed into Jupiter.
直到现在，人们都认为彗星是唯一一个还撞击木星的天体。
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