Jupiter, the fifth
planet from the Sun, is by far the most massive planet (see solar system). Its mass represents more than
two-thirds of the total mass of all the planets, or 318 times the mass of the Earth. If Jupiter had been several times more massive, it would have been a star, because the pressure and temperature at its center would have been great enough to set off nuclear fusion. Because Jupiter's density (1.3 g/cm7, or 82 lb/ft7) is relatively low, it has the volume of 1,000 Earths. Jupiter is 1,000 times smaller than the Sun. The
planet's fast axial rotationÑonce every 9 hr 55.5 minÑcauses it to be considerably flattened: the equatorial diameter is 142,800 km (88,700 mi), but the
distance from the north to south pole is only 133,500 km (83,000 mi). Jupiter orbits the Sun in 11.9 years at a distance of 778.3 million km (483.3 million mi), or 5.2 times the Earth's distance from the Sun.