On July 25, 1976, the Viking 1 spacecraft captured images of a mesa in the Cydonia region of Mars with the appearance of a humanoid face (see inset), which led to much speculation about life on Mars. In 2007, high-resolution images taken by the Mars Reconnaissance Orbiter of the same structure definitively showed that the face was merely an optical illusion known as pareidolia.Photo: NASA/JPL/University of Arizona