Perhaps in hope of stunning revelation, the image was digitally enhanced by engineers and computer specialists, and was soon followed by reports of pyramids in close proximity to the face. NASA officially dismissed these features as a “trick of light and shadow”, and the result of random natural forces such as wind and erosion; but this explanation was quickly countered by accusations of a cover-up. One researcher calculated a striking similarity between the distribution of these monuments and the astronomical constellation of Orion, as it would have appeared from Mars 500 thousand years ago. From this he then reasoned that the face was artificial, erected by an extra-terrestrial civilization half a million years ago, and intended to resemble a human (this human resemblance is apparently evidence of an alien visitation to our planet in our distant past).

But skeptics have proposed that maybe the face and its human resemblance are merely a by-product of our evolutionary history, which has selected for desirable traits such as face recognition and the ability to decipher familiar patterns from random noise. From the beginning of infancy, we can recognize faces and respond with a grin. And our requirements for face recognition are remarkably few, which is evident when we associate a curved line with two strategically placed dots as a face with an implied mood. So given 150 million square kilometers of Martian surface area, it is hardly surprising that features resembling a face were eventually encountered on Mars. In fact, it would be surprising if they weren’t encountered.

And other faces have been found too. There is a happy face inscribed on a Martian impact crater, with a set of radial splash marks giving it the appearance of a smiling sun. And there is a lava flow with a shape reminiscent of Kermit the Frog. But the face on Mars stands out because, while these other features have precise geological explanations, the face has only a vague one – it is simply an unusual geological landform, carved over the years by the random forces of nature, and enhanced under certain lighting conditions when the sun is very low in the horizon.

The most suggestive image of the face shows one side lit by the sun and the other in deep shadow. But when we severely enhance the contrast in the shadow we see that the face is at best half a face. And when we study this [half] face in more detail, we find that a strategically placed nostril which adds much to the impression of the face is actually a black dot corresponding to lost data from the radio transmission from Mars to Earth.

In August 1993 there was hope that the Mars Observer spacecraft would shed new light on the face debate. Onboard, it had a camera that could give 1.5-meter resolution of the Martian surface, and was scheduled to fly over the Martian region of Cydonia (where the face is located). But unfortunately NASA scientists lost contact with the spacecraft just before it achieved orbit. This was followed by accusations against NASA for faking the mishap, perhaps so that they could study the face in more detail without sharing their knowledge with the public, who were to be kept ignorant of an extraterrestrial presence in our own solar system. But others have suggested that it is the evil Martian beings who wish to hide their own existence from humanity. Or maybe the failure could be due to a couple of faulty transistors that stopped working after spending years in space.

Nevertheless, in April 1998 this goal was fulfilled when the Mars Global Surveyor resurveyed the site of the supposed face, this time in about ten times as much detail and with the face fully illuminated. And what it uncovered was much less face-like. In fact, it looked more like an apron or a shield than a face. It is now unanimously agreed that the face is at best half a face; but admittedly, there is still a small possibility that  it is a weathered artifact from an ancient Martian civilization. And perhaps partly driven by a rebellion against the clear overconfidence of skeptics, the believers have argued for the significance of the face’s good side, identifying its potential nostrils, teeth, mouth and eyebrow ridge, among various other features. But the skeptics have replied that these features are instead evidence of a type of illusion or misperception called pareidolia, in which a vague stimulus is clearly perceived as something it is not. Finding a face on Mars may be no different from finding a face in the clouds. But regardless of its true origin, it is a reflection of our imagination and our desire to find life elsewhere in the universe, and perhaps an expression of our cosmic loneliness, that sustains our wonder and keeps us searching for an answer.