<P> The atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula . Neon in the upper atmosphere only consists of 20 parts per million by mass, which is about a tenth as abundant as in the Sun . Helium is also depleted to about 80% of the Sun's helium composition . This depletion is a result of precipitation of these elements into the interior of the planet . </P> <P> Based on spectroscopy, Saturn is thought to be similar in composition to Jupiter, but the other giant planets Uranus and Neptune have relatively less hydrogen and helium and relatively more ices and are thus now termed ice giants . </P> <P> Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined--this is so massive that its barycenter with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's center . Jupiter is much larger than Earth and considerably less dense: its volume is that of about 1,321 Earths, but it is only 318 times as massive . Jupiter's radius is about 1 / 10 the radius of the Sun, and its mass is 0.001 times the mass of the Sun, so the densities of the two bodies are similar . A "Jupiter mass" (M or M) is often used as a unit to describe masses of other objects, particularly extrasolar planets and brown dwarfs . So, for example, the extrasolar planet HD 209458 b has a mass of 0.69 M, while Kappa Andromedae b has a mass of 12.8 M . </P> <P> Theoretical models indicate that if Jupiter had much more mass than it does at present, it would shrink . For small changes in mass, the radius would not change appreciably, and above about 500 M (1.6 Jupiter masses) the interior would become so much more compressed under the increased pressure that its volume would decrease despite the increasing amount of matter . As a result, Jupiter is thought to have about as large a diameter as a planet of its composition and evolutionary history can achieve . The process of further shrinkage with increasing mass would continue until appreciable stellar ignition was achieved, as in high - mass brown dwarfs having around 50 Jupiter masses . </P>

What is the size of the planet jupiter
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