Fifth planet (hypothetical) into the Sun. Unlike the Disruption Theory's fifth planet, "Planet V" is not credited with creating the asteroid belt. The concept of a fifth planet which had been destroyed to make the asteroid belt, as in the Disruption Theory, has been a popular one in fiction. Fifth planet (hypothetical) In the history of astronomy, a handful of Solar System bodies have been counted as the fifth planet from the Sun. Under the present definition of a planet, Jupiter is counted as the fifth. There are three main ideas regarding hypothetical planets between Mars and Jupiter. During the early 19th century,
Solar System disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes the zodiacal light. It was likely formed by collisions within the asteroid belt brought on by gravitational interactions with the planets. The second dust cloud extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt. The inner Solar System is the region comprising the terrestrial planets and the asteroid belt. Composed mainly of silicates and metals, the objects of the inner Solar System are relatively close to the Sun; the radius