There was probably a lot more material between Mars and Jupiter billions of years ago, but it either got eaten by Jupiter, or the planet's immense gravity altered the asteroids' orbits, flinging them away.

几十亿年前，火星和木星之间可能有更多的物质，但它们不是被木星吞噬了，就是巨大的引力改变了小行星的公转轨道，把它们甩了出去。