Asteroid belt

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asteroid belt

The asteroid belt or main belt is a ring of small and large rocks and dust between the orbits of Mars and Jupiter. The biggest object in the asteroid belt is Ceres, a dwarf planet. Most asteroids orbit at 2 to 3 times the distance between Earth and the Sun. Planets that are "inside" - or before - the asteroid belt (which means they are closer to the sun) are called inner planets. Planets that are "outside" - that is, after - the asteroid belt are called outer planets: so Mercury, Venus, Earth, and Mars are inner planets, while Jupiter, Saturn, Uranus and Neptune are the outer planets.

Origin

The asteroid belt looks a lot like the orbit of a planet. There may be a reason for this. There is some evidence that there used to be a planet that orbited the sun between Mars and Jupiter. It might have exploded, and the asteroids in the asteroid belt may be the remains of that planet.

The idea that there was once a planet between Mars and Jupiter that exploded to become the asteroid belt is called the Exploded Planet Hypothesis (a hypothesis is an idea that may or may not be true). The Exploded Planet Hypothesis has several reasons to support it. Firstly, if a terrestrial planet exploded, pieces that flew into space would look like rocks and ice. Our planet is made of mostly water, so if it exploded, it would send millions of tons of water into space, and this water would become ice, maybe making really big comets.

More reasons that might support this hypothesis are the crater scars on many planets and moons. When a very large meteorite hits a planet or a moon, it leaves a crater (a big dent in the surface). However, some scientists argue that the meteroites hit the planets and moons randomly over many, many years, and some say that the Exploded Planet Hypothesis could not be true because there are not enough asteroids in the asteroid belt to make up a whole planet. Those who think the Exploded Planet Hypothesis is true, however, say that if all the comets and other objects in the solar system that look like they come from a planet were counted, this exploded planet would be much bigger than the earth.

Formation

The asteroid belt failed to form a planet because of Jupiter's gravity. The belt used to contain many more asteroids than it does today, but Jupiter's gravity disturbed the orbiting debris and much of it was sent into orbits which meant it was lost to the asteroid belt. The total mass of the material in the asteroid belt today is thought to be about 4% of the mass of the Earth's Moon.