Atmosphere of Mercury Atmosphere of Mercury Mercury has a very tenuous and highly variable atmosphere (surface-bound exosphere) containing hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10 bar (1 nPa). The exospheric species originate either from the Solar wind or from the planetary crust. Solar light pushes the atmospheric gases away from the Sun, creating a comet-like tail behind the planet. The existence of a Mercurian atmosphere had been contentious before 1974, although by that time a consensus had formed that Mercury, like the Moon, lacked any substantial atmosphere. This conclusion was confirmed in 1974
Atmosphere of Uranus bright tropospheric clouds are rare on Uranus, probably due to sluggish convection in the planet's interior. Nevertheless, observations of such clouds were used to measure the planet's zonal winds, which are remarkably fast with speeds up to 240 m/s. Little is known about the Uranian atmosphere as to date only one spacecraft, "Voyager 2", which passed by the planet in 1986, obtained some valuable compositional data. No other missions to Uranus are currently scheduled. Although there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous envelope (the region accessible to remote sensing) is called its