
Astronomers sometimes divide the Solar System structure into separate regions. The includes Mercury, Venus, Earth, Mars, and the bodies in the . The includes Jupiter, Saturn, Uranus, Neptune, and the bodies in the . Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct r.

Natural resources such as , (crude oil) and take thousands of years to form naturally and cannot be replaced as fast as they are being consumed. It is projected that fossil-based resources will eventually become too costly to harvest and humanity will need to shift its reliance to such as solar or wind power. An alternative hypothesis is that carbon-based fuel is virtually inexhaustible in human terms, if o.