Venus has come from radio signals transmitted by spacecraft that have landed on the surface. Surface temperatures are about 500 degrees centigrade. The atmosphere is composed of carbon dioxide, which traps much of the Sun's radiation.
Broad plains dotted with thousands of low‐viscosity basaltic shield volcanoes cover about 80 percent of the surface. Steep‐sided volcanic structures resembling felsic lava domes on Earth suggest that felsic magmas may occur. Rocks analyzed by a Russian spacecraft contained high potassium concentrations, also suggestive of felsic magmatic differentiation.
Radar mapping of the surface has identified elongate mountain ranges that seem to have been formed by extension and compression, possibly as a result of plate tectonic activity or mantle convection and mantle plumes.