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。

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These "dirty snowballs" castoff gas and dust whenever they venture near the sun.

这些“脏雪球”在冒险接近太阳时会丢出气体和尘埃。

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They are now seen as "icy dirtballs", dominated by rock, in contrast to the "dirty snowballs" hypothesised by Fred Whipple, an astronomer at Harvard University, in 1950.

现在彗星被认为是一个主要由岩石构成的冰冷的土球。 而不是1950年哈佛大学天文学家Fred Whipple假设的盖着土的冰球。

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While certainly spectacular and ethereal in appearance, comets are essentially "big, dirty snowballs" flying through space.

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During this violent time, much of the debris would have resembled comets - dirty snowballs thought to be mostly slushy water surrounding a rocky core - slamming into Earth at velocities greater than 25 km per second (16 miles per second).

BBC: Comets could have seeded life on Earth