What is the solar system? It is our Sun and everything that travels around it. The Sun is in the center of the solar system. Our solar system is always in motion. Eight known planets, along with comets, asteroids, and other space objects orbit the Sun. The Sun is the biggest object in our solar system. It contains more than 99% of the solar system's mass. Nearest the Sun are four fairly small, rocky planets - Mercury, Venus, Earth and Mars. On the...