Why are Jovian planets bigger?
All planets did not have the same original matter composition. The farther from the Sun, the more water was in the form of ice. Ice helped the dust and rock to accrete more matter in the primordial solar system. These outer planetoids most likely formed earlier and accreted matter more quickly than inner planets where water was in gas or liquid form. When the protosun ignited in nuclear fusion, it sent out a blast of solar wind blowing the lighter gasses and elements out from the inner planets. The outer planets had the gravity to capture this material making them even larger. Without these gasses, we estimate that the core of Jupiter is the size of 15 Earths.
