Plan view of the Solar System, showing the orbits of the planets and asteroids to scale with respect to each other. The planets themselves are also to scale with each other but not relative to the orbits - compared to the latter the planets would be invisible. The innermost planets, Mercury to Mars, are huddled very close to the Sun, within 1.6 astronomical units (1 AU = Earth-Sun distance). The giants, meanwhile, are an order of magnitude further out, with Neptune, the outermost world, fully 30 times the distance from the Sun that Earth is. The giants and the rocky inner planets are separated by a vast, sparse reservoir of Solar System debits, the asteroid belt.