The Uranian atmosphere can be divided into three main layers: the troposphere, between altitudes of −300[lower-alpha 1] and 50 km and pressures from 100 to 0.1 bar; the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0.1 and 10−10 bar; and the hot thermosphere (and exosphere) extending from an altitude of 4,000 km to several Uranian radii from the nominal surface at 1 bar pressure.[1] Unlike Earth's, Uranus's atmosphere has no mesosphere.