The solar system consists of the sun and objects that orbit it, including 8 planets, asteroids, meteorites, and comets. The sun is at the center and is made primarily of hydrogen and helium. It has a diameter of 1.38 million km and a surface temperature of around 10,000°F. The planets can be divided into terrestrial planets of Mercury, Venus, Earth, and Mars, which are rocky, and gas giants of Jupiter, Saturn, Uranus, and Neptune, made mostly of hydrogen and helium. Kepler's laws describe planetary motion as elliptical orbits with the planet moving faster when closer to the sun.