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。

youdao

The big planet throws a lot of comets out of the solar system, but it also throws them in.

这个大魔头向太阳系外扔了很多扫帚星，但又把它们引向了太阳系内部。

youdao

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。

youdao

The goal of the Stardust-NExT spacecraft is to gather scientific evidence about one of the solar system's most changeable objects -- comets.

VOA: special.2011.02.09

Astronomers have recently found some surprising evidence that some of those materials may have come from comets.

VOA: special.2009.09.30

It says an explosion or explosions by comets could explain the disappearance of many animals and human beings who lived in North America at that time.

VOA: special.2009.01.20

In its journey through space, Earth is bombarded by a hailstorm of comets, meteors and asteroids.

WSJ: Asteroid to Narrowly Miss Earth Next Week

The data are the orbits of comets that are likely to have been first-time visitors to the inner solar system.

ECONOMIST: X marks the spot

Some astronomers seemed to think that he and his colleagues had been too selective about the sample of comets they studied.

ECONOMIST: X marks the spot