In one of the images taken by Viking 1 on July 25, 1976, one of the Cydonian mesas, situated at 40.75° north latitude and 9.46° west longitude, had the appearance of a humanoid "Face on Mars". When the image was originally acquired, Viking chief scientist Gerry Soffen dismissed the "face" in image 35A72 as a "[trick] of light and shadow". However, a second image, 70A13, also shows the "Face" and was acquired 35 Viking orbits later at a different "sun-angle" than the 35A72 image. This latter discovery was made independently by two computer engineers at NASA's Goddard Space Flight Center, Vincent DiPietro and Gregory Molenaar, who discovered the two misfiled images, Viking frames 35A72 and 70A13, while searching through NASA archives. The occurrence of an object on Mars with a seemingly human face caught the attention of individuals and organizations interested in extraterrestrial intelligence and visitations to Earth, and the images were published in this context in 1977. Some commentators, most notably Richard Hoagland, believe the "Face" to be evidence of a long-lost Martian civilization along with other features they believe are present, such as apparent pyramids, which they argue are part of a ruined city. Image analysis of the original Viking images led a few researchers to suggest that the features of the "Face" might not be an accidental consequence of viewing conditions. Astronomer Carl Sagan criticized much of the speculation about the "Face" in an eponymous chapter of his book The Demon-Haunted World. 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 have included 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 afford much improved resolution. For instance, the Mars Express images are at a resolution of 14 m/pixel (46 ft/pixel) or better. By combining data from the High Resolution Stereo Camera (HRSC) on the Mars Express probe and the Mars Orbiter Camera (MOC) on board NASA's Mars Global Surveyor it has been possible to create a 3D representation of the "Face on Mars". Today, the "Face" is generally accepted to be an optical illusion, an example of pareidolia. After analysis of the higher resolution Mars Global Surveyor data NASA stated that "a detailed analysis of multiple images of this feature reveals a natural looking Martian hill whose illusory face-like appearance depends on the viewing angle and angle of illumination".[24] Similar optical illusions can be found in the geology of Earth; examples include the Old Man of the Mountain and the Badlands Guardian, which resembles a human head wearing a Native American headdress. Aside from speculation concerning their artificial origins, Cydonia and the "Face on Mars" also appear frequently in popular culture, including feature films, television series, videogames, comic books, and even music. http://nssdc.gsfc.nasa.gov/planetary/viking.html