Happy 36th, Face on Mars!

Above is a composite of two images taken of the Cydonia region of Mars. The first image (left) was taken July 25, 1976 by NASA's Viking 1 Orbiter (image F035A72). The image includes the feature which came to be known as "the Face on Mars." Image Credit: NASA/JPL-Caltech. The second image (right) was taken April 8, 2001 by Mars Global Surveyor and is a high-resolution view of the same feature (image PIA03225). Image Credit: NASA/JP/Malin Space Science Systems

July 25th marks the 36th anniversary (July 25, 1976) of the first imaging of the Cydonia mesa of Mars (40.75° north latitude and 9.46° west longitude). The image (F035A72) was taken by the recently-arrived Viking 1 Orbiter and included several interesting features. One of these, roughly 2 km (1.2 miles) in length, came to be known as "the Face on Mars."

When the image was acquired (F035A72), Viking chief scientist Gerry Soffen dismissed the "face" in the image as a "trick of light and shadow." However, a second image, F070A13, also showed the "Face," and was acquired 35 Viking orbits later at a different sun-angle from the F035A72 image. This latter discovery was made independently by Vincent DiPietro and Gregory Molenaar, two computer engineers at NASA's Goddard Space Flight Center. DiPietro and Molenaar discovered the two misfiled images while searching through NASA archives.

The Face on Mars became one of the most striking and remarkable images taken during the Viking missions. Resembling a human face, the image caused many to hypothesize that the feature was the work of an extraterrestrial civilization.

More than 20 years after the Viking 1 images were taken, a succession of spacecraft visited Mars and collected new data from the Cydonia region. These spacecraft include NASA's Mars Global Surveyor (1997–2006) and Mars Reconnaissance Orbiter (2006-), and the European Space Agency's Mars Express probe (2003-). In contrast to the relatively low resolution of the Viking images of Cydonia, these new platforms had much improved resolution. After analysis of the higher resolution data, NASA stated that the feature was revealed to be a natural looking Martian hill whose illusory face-like appearance depended on the viewing angle and angle of illumination.

Similar optical illusions can be found in the geology of Earth. Examples of such optical illusions include the Old Man of the Mountain, the Pedra da Gávea, the Old Man of Hoy and the Badlands Guardian.

To learn more about NASA's ongoing Mars Exploration Program, visit mars.jpl.nasa.gov .

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