Uranus
Uranus is the seventh planet from the Sun. Its name is a reference
to the Greek god of the sky, Uranus, who according to Greek
mythology, was the great-grandfather of Ares. It has the
third-largest planetary radius and fourth-largest planetary mass
in the Solar System.
The standard model of Uranus's structure is that it consists of
three layers: a rocky (silicate/iron–nickel) core in the center,
an icy mantle in the middle and an outer gaseous hydrogen/helium
envelope. The core is relatively small, with a mass of only 0.55
Earth masses.
The composition of Uranus's atmosphere is different from its bulk,
consisting mainly of molecular hydrogen and helium. The helium
molar fraction, i.e. the number of helium atoms per molecule of
gas, is 0.15±0.03 in the upper troposphere.
