Our solar system has four inner rocky worlds, four gaseous outer worlds, plus icy Pluto. All are in the same orbital plane, except Pluto. Pluto’s small size and odd characteristics lead some astronomers to believe that it’s not a planet but a comet-like object captured from the outer solar system. The similar orbits of the planets in the solar system result from conditions that prevailed inside the disk of gas and dust from which they formed.