User:Sopmore jjones

a typical single star that is itself in orbit about the center of the Milky Way Galaxy. Nearly all of the other bodies in the solar system—the terrestrial planets, outer planets, asteroids, and comets—revolve on orbits about the Sun. Various types of satellites revolve around the planets; in addition, the giant planets all have orbiting rings. The orbits for the planets appear to be fairly stable over long time periods and hence have undergone little change since the formation of the solar system. It is thought that some 4.56 × 109 years ago a rotating cloud of gas and dust collapsed to form a flattened disk (the solar nebula) in which the Sun and other bodies formed. The bulk of the gas in the solar nebula moved inward to form the Sun, while the remaining gas and dust are thought to have formed all the other solar system bodies by accumulation proceeding through collisions of intermediate-sized bodies called planetesimals. Planetary systems are believed to exist around many other stars in the Milky Way Galaxy. Solid evidence for the existence of Jupiter-mass planets around nearby solarlike stars now exists. See also planet