In 1976, the Viking 1 mission began taking photographs of the surface of Mars, in part to find landing sites for future missions, and also to get a better idea of what Mars was like, to determine the ages of various parts of Mars (done by counting craters, which assumes that once the great bombardment was over, the impacts were more or less regular over time if we think in terms of geological timing.) On the Cydonia Mensae, an image came back that, when refined, looks surprisingly like a face carved into a large rock. Two points are worth mentioning. The first is, if it were such a head, the angle of the light only allows you to see the right side of the head; the rest is in deep shadow. The second is all we received of this object was 64 pixels. The “face” is clearly a butte standing up from the surface (and there are lot of these in the region) and it is about 2.5 km long, about 1.5 km wide, and something like up to 800 m above the average flat ground at its highest point. As you might imagine, with only 64 pixels, the detail is not great, but there is a crater where the right eye should be, a rise that makes the nose, and some sort of “crack” or depression that hints at a mouth, but most of the “mouth” would be in the shade, and hence would be invisible. The image was also liberally splattered with black spots; these were “failed pixels” i.e. a transmission problem. What you see below is that primary image.
So, what was it? The most obvious answer was a rock that accidentally looked like a face. To the objection, what is the probability that you could end up with that, the answer is, not as bad as you might think. There are a lot of mesas and rock formations on Mars, so sooner or later one of them might look like something else. There are a number of hills etc on Earth where you can see a head, or a frog, or something if you want to. If you think about it, an oval mesa is not that improbable, and there are a lot of them. There are a very large number of impact craters on Mars, so the chances of one being roughly where an eye would be is quite high (because there is quite a bit of flexibility here) and there are really only two features – the eye and the “mouth”. The rise for the nose only requires the centre to be the highest part, and that is not improbable. As it happens, when you see the whole thing, the left side of the head has sort of collapsed, and it is a fracture offshoot from that collapse that gives the mouth.
However, the image caught the imagination of many, and some got a little carried away. Richard Hoagland wrote a book The Monuments of Mars: A City on the Edge of Forever. If nothing else, this was a really good selling book, at one stage apparently selling up ot 2000 copies a month. Yep, the likes of me are at least envious of the sales. So, what did this say? Basically, Hoagland saw several “pyramids” near the Face, and a jumble of rocks that he interpreted as a walled city. Mars had an ancient civilisation! Left unsaid was why, if there were such “Martians” did they waste effort building pyramids and carving this Face while their planet was dying? For me, another question is why does something this fanciful become a best seller, while the truth languishes?
So what caused this? I don’t know, and neither does anyone else. It is reasonably obviously caused by erosion, but what the eroding agent was remains unknown. If you believe Mars once had an ocean, the Cydonian region is roughly where one of the proposed shorelines was. It could also be caused by glaciation, or even wind erosion, aided by moisture in the rock. The freezing/thawing of water generates very powerful forces. What we need is a geologist to visit the site to answer the question, although there would be far more important things to do on Mars than worry about that rock.
Suppose it was carved by a civilization? I included that possiblity in my novel Red Gold. In this, one character tried pulling the leg of another by announcing that it was “obviously carved” by aliens with the purpose of encouraging humans to go into space. “It is worth it,” the aliens would be saying. So why is it so rough? Because the aliens were plagued by accountants, who decided that the effort to do it properly was not worth the benefit; if humans cannot take the hint from the roughly hewn rock, so be it.
It also figures in another of my novels: A Face on Cydonia. Again, it is intended as a joke in the book, but on whom? Why did I do that? Well, I started writing when I heard that Global Surveyor was going to settle this issue, so I thought I should try to have something ready for an agent. However, Global Surveyor, which took very narrow strip images, and could have taken two years to cover this area, took only a few weeks. Out of luck again! Fortunately, the story was never really about the rock, but rather the effect it had on people.
A quick commercial: if anyone is interested, the ebook is at 99 cents on Amazon (or 99p) for the first week of September. The book is the first of a trilogy, but more about people being taken to levels higher than their abilities, and also about what causes some to descend to evil. It also has just a toiuch of science; while you can ignore this and just consider it a powerful explosive, it has the first mention of a chemical tetranitrotetrahedrane. That would be a really powerful explosive, if it could be made, but the more interesting point is why is that there?