In 1976, the Viking 1 orbiter began to take a series of high resolution photographs of the Martian surface in areas which were candidates for landing sites for the lander portion of the mission. The pictures were taken at a very low sun angle to reveal the presence of large obstacles which might damage a landing spacecraft. On July 25th, 1976 during orbit 35, the orbiter imaged a peculiar feature near the eastern edge of the albedo feature Mare Acidalium, at 41N, 9.5W, north of Cydonia Mensae. From certain angles, the mesa-like feature tends to resemble a mask-like face, with two unequal eyes and a bent mouth surrounded by a sloping plateau making up the rest of the head. It is about 2.6 km (1.63 mi) long, 2 km wide (1.25 mi), and nearly 250 meters (820 ft) high at its highest point.

On orbit 70, the "face" was again imaged under a higher sun angle, and showed slightly more detail. In the second view, the right "eye" is seen as being somewhat smaller than the left one, and is located further below the level of the left one, thus giving the "face" a rather distorted look. A bulge or mound is visible just above the left eye's outline, showing that much of the left "eye" is just a shadow cast by this mound. The mouth's eastern side is poorly shown, and seems to be bent at nearly a 45 degree angle to the line of the western side of the mouth. The entire northeast half of the "face" appears to have a more constant slope than the southwestern side, making the entire feature look more like a crude child's drawing than a monument. In Martian geologic terminology, the "face" is known as a "knob", a remaing outcropping of rock after erosion has removed less dense material. The low sun angle exagerates the relief of the feature, making it look more pronounced than it really is. Numerous other butte or mesa-like features are present in the area, but the so-called "city" just to the west of the "face" appears to be just a cluster of mountain-like knobs.

The original Viking orbiter images containing the most detailed views of the "face" are picture number (PICNO) 35A72 at 47 meters/pixel scale, and number 70A13 at 43 meters/pixel scale. Since it takes at least two pixels to "resolve" a surface feature, the true maximum surface resolution of these two images is probably closer to 100 meters. These images are available from NASA, and on several websites on the Internet. One location containing the images and a detailed discussion on the face can be found on the FACE ON MARS page at: http//barsoom.mss.com/education/facepage/face.html. Some people took the original raw images and did enlargment and some enhancement in a way which introduced non-existant detail below the true resolution limit of the Viking camera (such as "teeth" in the mouth). Such modified images are basically useless for a serious study of this face-like feature.

On April 5th 1998, the Mars Global Surveyor imaged a strip of Mars which included the location of the "face". With resolution ten times higher than that of the Viking images, the picture was taken with a much higher sun angle (about 25 degrees high, roughly from the southeast) to reveal the true nature of the feature. An additional even higher resolution (2 meters/pixel) image was taken on April 8th, 2001, with the sun from the southwest. The images showed a somewhat eroded low dome-like mesa, with a sloping outer edge, sinuous cracks, some sharper ridges, and irregular blocky terrain with scattered large rocks and boulders which shows no sign of the feature being anything but a natural one. MOLA laser altimeter readings confirmed the height at about 244 meters (800 ft), with little in the way of large vertical relief to suggest that the previously-viewed face-like features were anything but low-sun shadow effects. Considerable fine detail is visible in the MGS images, but it takes some imagination (at least, initially), to make this feature resemble a face. Fine radial (possibly erosional) patterns are clearly visible over much of outer rim of the "face". The western half of the "mouth" is a shallow depression between two ridges, and is somewhat irregular in form. No "teeth" are seen in the mouth in the locations indicated by some of the faulty Viking image inhancements, and the "mouth" portion abruptly ends in the middle of the face with a blocky ridge. Indeed, much of the eastern half of the mouth seems not to be present, again showing that much of this feature was a mere shadow. Only the "nose" seems to show up prominently, and it only appears as a very rocky broad ridge with a deep sinuous crack outlining its eastern edge. The area around the where the left "eye" appeared in the Viking images shows only a shallow depression open to the west, formed by a partially-encircling low ridge on the east and north which has a nice flat-topped bulge to cast an "eye-shadow", when the sun is low in the west. The right eye is very difficult to discern with any certainty, since a portion of it appears to be one of the sinuous cracks on the "face's" eastern side. The "eyes" seen the original images are clearly more shadow effects than real topographic features.

The "face" in the original Viking images looks more like that of a monkey than of a man, and any "face" in the MGS image looks more like a Lion than a human. FACE MESA is still an interesting feature, and will probably trigger more interest as the years go by.

Comparison of Viking and Observer Images (107KB)