From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Solar System (太陽系, Taiyōkei) is the name of a star system.
As in the real world, there were millions, perhaps billions, of star systems within the four galaxies. Unlike in the real world, there was known life among these planets.
Dragon Ball Z
The Solar System consisted of the Sun and the astronomical objects gravitationally bound in orbit around it. Only Planet Earth, Planet Mars, Planet Jupiter, Planet Saturn, and Planet Venus appeared, but it could be presumed that all eight planets existed.
The Solar System was most notably mentioned during the battle against Cell when the maniacal Artificial Human created what he called the Solar Kamehameha and stated that the energy beam not only had enough energy to destroy Planet Earth, but the entire Solar System.