Snow are able to grow to hundreds of micrometers or millimeters in size at the expense of the water droplets by the Wegener–Bergeron–Findeisen process. The corresponding depletion of water vapor causes the ice crystals to grow at the droplets' expense. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their mass, and may collide and stick together in clusters, or aggregates. These aggregates are snowflakes, and are usually the type of ice particle that falls to the ground. Although the ice is clear, scattering of light by the crystal facets and hollows/imperfections mean
Atmosphere of Pluto Pluto. The question of composition was answered in 1992 via infrared spectra of Pluto by the 3.8-meter United Kingdom Infrared Telescope. The surface of Pluto turned out to be covered mainly by nitrogen ice. Since nitrogen is, in addition, more volatile than methane, this observation implied a prevalence of nitrogen also in the atmosphere (although gaseous nitrogen was not seen in the spectrum). Furthermore, a small admixture of frozen carbon monoxide was discovered. The same year observations by the 3.0-meter NASA Infrared Telescope Facility revealed the first conclusive evidence of gaseous methane. Understanding the state of the atmosphere requires knowing