The Face on Mars press release

On 31 July 1976 NASA released a Viking photo of a mesa on Mars that looks like a face. Later writers argued it was an artificial structure.

NASA released the Viking picture on 31 July 1976 with a press release describing a formation that looks like a human head. The photograph had been taken on 25 July at a distance of 1873 kilometers, while planners searched for landing sites, and NASA chose to publish it to stir public interest in Mars and spaceflight. The caption said the scene held eroded mesa-like landforms. A big rock shape in the centre, a mile across, looks like a head because shadows suggest eyes and a nose and mouth. The speckled look came from bit errors that enlargement emphasised, and the sun stood at roughly 20 degrees.

NASA scientists had already read the picture as an illusion of optics, produced by the sun's angle. Skeptoid says that the idea of a made sculpture would probably never have spread without Richard Hoagland's writing. On seeing the picture he concluded that a deliberate carving was the sole reasonable reading, and his book Monuments of Mars claimed the Cydonia face was one of numerous artificial structures there, among them pyramids and entire cities.