The most famous of all extraterrestrial human-like features was first described as appearing to have eyes and nostrils by scientists at NASA's Jet Propulsion Laboratory in 1976. But the feature was revealed by subsequent photographs to be a rather mundane mountain whose striking facial features depend on sunlight hitting it at a certain angle. The speckled appearance of the image is due to missing data, called bit errors, caused by problems in transmission of the photographic data from Mars to Earth. Bit errors comprise part of one of the 'eyes' and 'nostrils' on the eroded rock that resembles a human face near the center of the image. Shadows in the rock formation give the illusion of a nose and mouth.
Planetary geologists attribute the origin of the formation to purely natural processes.