Comets and asteroids Short period comets Comets that come round and round again have been trapped by Jupiter's gravity. Compare their elongated and tilted orbits, with the near circular orbits of the planets. Asteroids in orbit Thousands of asteroids swarm around the solar system. They are mainly concentrated between Mars and Jupiter, but see how Earth can find itself uncomfortably close to asteroids on more eccentric orbits.. The Kuiper belt Beyond Neptune, on the far-flung edge of the planetary system, a new asteroid belt is being explored following the first discovery in 1992. See for yourself the tracks of these ice dwarfs so recently found. See also: The Essentials Sun, Moon and Earth The Planets Sights in the sky Spaceflight