J upiter, the fifth planet from the Sun, is by far the most massive planet. Its mass represents more than two-thirds of the total mass of all the planets, or 318 times the mass of the Earth.
J upiter could have possibly become a star is if was several times more massive, because it would have had high enough temperatures and pressure to start nuclear fusion reactions. Because Jupiter's density (1.3 g/cm3), or 8 is relatively low, it has the volume of only 1,000 Earths. It is much less dense than the Sun, almost 1000 times. The planet's fast rotation, once every 9 hr 55.5 min, causes it to be considerably flattened.
J upiter orbits the Sun in 11.9 earth years at a distance of 778.3 million km (483.3 million miles), or 5.2 times the Earth's distance from the Sun. Although Jupiter was not large enough to become a star, the compression caused by the planet's gravity caused the planet to become very hot. Even today Jupiter radiates almost twice as much heat as it receives from the Sun.