Why does Earth only have one moon, and why is it so large comparatively

Why questions are always fun, especially ones like this, where we really don't have any idea. One theory is that the Earth and Moon are large enough that over a long period of time, any large third body in the system would have been in an unstable orbit. Another is that Earth and Moon just swept up the small debris, comets, and small asteroids in the vicinity. We know the Moon has had lots of impacts, and we have to imagine the Earth has too, but atmosphere has incinerated many of them, while weathering has eroded evidence of many others.

It may be that the Moon actually formed from such a collision. I find it hard to remember back when it happened, though ;-))

Even Jupiter couldn't an asteroid big enough to get a new moon, how come Earth will do it. Even if it does do you think it come all the way a long distance in space and suddenly fall into a orbit around the Earth. No, it will hit it. If something even like in size half of our present moon hits the Earth, Earth will with a 99.99% chance break. Then you can live on one part and I on the other, that is if we survive.

That's funny, folks on the moon wonder why they only have one 'earth' and why it's so small compared to Jupiter.
like Einstein said (and all my aunts, uncles, cousins and nephews as well) :" Everything's relative."