Jupiter and liquid matter. It is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of at its equator. The average density of Jupiter, 1.326 g/cm, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiter's upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules. A helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiter's
HR 8799 e HR 8799 e </math></ref> HR 8799 e is a large exoplanet, orbiting the star HR 8799, which lies 129 lightyears from Earth. This gas giant is between 5 and 10 times the mass of Jupiter, the largest planet in the Solar System. Due to their young age and high temperature all four discovered planets in the HR 8799 system are large, compared to all gas giants in the Solar System. HR 8799 e is the fourth planet orbiting HR 8799 in order of discovery. It is a young, hot and massive gas giant, and is fairly close to its star,