Geochemistry source for chemical abundance, despite their rareness (only five have been recovered on Earth). The planets of the Solar System are divided into two groups: the four inner planets are the terrestrial planets (Mercury, Venus, Earth and Mars), with relatively small sizes and rocky surfaces. The four outer planets are the giant planets, which are dominated by hydrogen and helium and have lower mean densities. These can be further subdivided into the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune) that have large icy cores. Most of our direct information on the composition of the giant
Atmosphere of Uranus 50° latitude (first appeared in 2007) have grown more conspicuous since then. The atmosphere of Uranus is calm compared to those of other giant planets. Only a limited number of small bright clouds at middle latitudes in both hemispheres and one Uranus Dark Spot have been observed since 1986. One of those bright cloud features, located at −34° of latitude and called "Berg", probably existed continuously since at least 1986. Nevertheless, the Uranian atmosphere has rather strong zonal winds blowing in the retrograde (counter to the rotation) direction near the equator, but switching to the prograde direction poleward of ±20°