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 created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process. The Sun is growing brighter; early in its main-sequence life its brightness was 70% that of what it is today. The Solar System will remain roughly as we know it today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5 billion years from now. This will mark the end of the Sun's main-sequence life. At this time, the core of the Sun will contract with hydrogen