Albedo their reflectivities. Fresh 'black' ice exhibits Fresnel reflection. Snow on top of this sea ice increases the albedo to 0.9. Cloud albedo has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth." Albedo and climate in some areas are affected by artificial clouds, such as
Albedo feature regio. On bodies with a very thick atmosphere like Venus or Titan, permanent albedo features cannot be seen using ordinary optical telescopes because the surface is not visible, and only clouds and other transient atmospheric phenomena are seen. The "Cassini–Huygens" probe observed multiple albedo features on Titan after its arrival in Saturn's orbit in 2004. The very first albedo feature ever seen on another planet was Syrtis Major Planum on Mars in the 17th century. Today, thanks to space probes, very high-resolution images of surface features on Mars and Mercury are available, and the classical nomenclature based on albedo features