Neptune

From Triton's 5.866 day period of revolution around Neptune and its 220,000 mi (354,300 km) mean distance from it, astronomers estimated Neptune's mass to be 17.14 Earth masses, according to Kepler's third law. From Neptune's mean radius of 15,290 mi (24,625 km), a mean density (mass divided by volume) of 1.64 grams/cm³ was found. These values are similar to the ones found for Uranus. Uranus is slightly larger than Neptune, but Neptune is considerably more massive and denser than Uranus. Thus, Neptune is one of the Jovian planets, which are characterized by large sizes and masses but low mean densities (compared with Earth). The last characteristic implies that Jovian planets have extremely thick atmospheres and are largely or mostly composed of gases.

Neptune is in a nearly circular orbit around the Sun at a 30.1 astronomical unit (a.u.) mean distance (4,500,000,000 km) from it, making it the most distant known Jovian planet (and probably the most distant known major planet, since recent findings indicate that the Pluto-Charon system is too small to be considered a major planet) from the Sun. Kepler's third law gives 165 years for Neptune's period of revolution around the Sun. Therefore, Neptune will not have made one complete revolution around the Sun since its discovery until 2011.