An accidental discovery
On July 25, 1976, NASA's Viking 1 orbiter was busy scouting for a safe landing site for its sister craft, Viking 2. While photographing the northern latitudes of Mars, it captured frame 35A72. Buried within the image, in a region called Cydonia, was a rock formation that looked uncannily like a humanoid face. The mesa, a flat-topped, steep-sided hill, measured approximately 3 kilometers (1.9 miles) long and 1.5 km (0.9 miles) wide. Shadows cast by the low sun angle—about 20 degrees above the horizon—created the illusion of eyes, a nose, and a mouth.
NASA scientists correctly identified the feature as a natural landform, releasing the image with a caption noting its resemblance to a human head was a trick of light and shadow. The image quickly entered the public imagination, fueling speculation about ancient Martian civilizations. The effect is an example of a psychological phenomenon called pareidolia, the human brain's tendency to perceive familiar patterns, especially faces, in random stimuli. This cognitive shortcut is what allows us to see animals in clouds or a "man in the moon." The original Viking 1 image was also speckled with data transmission errors, known as bit errors, which coincidentally increased the "eye" and "nostril" features, further solidifying the illusion.
A clearer view
For over two decades, the "Face" was a staple of fringe theories, despite a second Viking 1 image taken 35 orbits later under a different sun angle showing the face had vanished. The arrival of a new generation of orbiters brought the feature into sharp focus. On April 5, 1998, the Mars Global Surveyor (MGS) captured an image of the Cydonia mesa with ten times the resolution of the Viking photos. The face resolved into a heavily eroded, natural-looking hill.
The MGS took an even more detailed photograph on April 8, 2001, from a distance of 450 kilometers (about 280 miles). This image had a resolution of about 2 meters (6.6 feet) per pixel, sharp enough to distinguish objects the size of a passenger jet. Later missions, including the European Space Agency's Mars Express in 2006 and NASA's Mars Reconnaissance Orbiter, provided even more data. The Mars Express's High Resolution Stereo Camera captured images with a resolution of 13.7 meters per pixel, allowing for the creation of 3D models of the landform. These subsequent observations confirmed that the "Face on Mars" is a completely natural mesa, one of many in the Cydonia region, which is a transition zone between the cratered southern highlands and the smoother northern plains of Mars.