Martian Archaeology. Not.

Well, it's a bit disappointing, but NASA's Curiosity rover has so far failed to confirm the presence of methane in the martian atmosphere. Other astronomers have claimed it's there, based on measurements made by orbiters and ground-based telescopes. A solid whiff of this smelly gas would be exciting, because it would hint at bacteria living underground.

However, for many people, the methane studies are irrelevant. Exhaust emissions from microbial Martians are simply beside the point. These folks have already found much better evidence for sophisticated life on the Red Planet: the dusty remains of advanced technology and complex animals, lying around in plain sight. It's all visible in photos taken by NASA rovers.

Even a brief perusal of such pictures, found in abundance on YouTube, will show you what are purported to be TV cables, a pipe, a toy car, a squirrel, martian prairie dogs, a socket wrench extender, a lug nut, hex nuts and wing nuts, a snake, an alien vehicle, a World War II Nazi helmet, a lizard, a duck, skeleton ribs, a fossilized Triceratops, and an alien posing on a rock like the Copenhagen mermaid.

It looks like a Red Planet yard sale. And remember: this is just the part of Mars falling under the gaze of rover cameras, an infinitesimally small fraction of the landscape. Imagine how much more treasure awaits our scrutiny.

Without doubt, discovering proof that Triceratops, Nazis and miscellaneous hardware were once present on the rocky landscapes of Mars is great fun. And you too can take part simply by going to the rover web sites, and looking around. Without doubt, you will espy critters and metal scrap.

But if you think that's what you're really seeing, you've been victimized by that soft, squishy organ between your ears. The problem is that your brain is wired up to see familiar objects (particularly things of importance, like faces and animals) with only minimal visual information. Think of emoticons: just a few lines and dots, and voila! You recognize a sad or smiling face.

The phenomenon of "seeing" familiar objects in natural settings (such as clouds) is called pareidolia. And given a choice between believing that NASA is deliberately ignoring front-and-center evidence for complex martian life, or ascribing all these claims to pareidolia... well, I vote for the latter.

At some level, of course, something that looks familiar might really be proof of deliberate construction. No one ever mistook New Hampshire's "old man of the mountain" for chiseled statuary; its sculptor was nature (also responsible for its collapse, a decade ago). But Mount Rushmore has an obviously unnatural history. It's clearly not a product of rock erosion, and indeed presents good evidence that someone was in the hills with pneumatic tools.

So what's the difference? When should we feel confident we've found something that's truly artificial, simply based on its appearance? Credibility depends on coherence and detail -- or putting it more scientifically, the information content of the image as defined by how much it departs from randomness. Consider your TV screen when there's no signal: just a canvas of random gray pixels. Nothing artificial there. But if a hi-def image of, say, Miley Cyrus pops up, you can safely say that it's the result of something deliberate and intelligent. Or at least deliberate.

A classic example of pareidolia is the well-known "Face on Mars." Originally spotted on a Viking orbiter photo in the 1970s, this feature in the Cydonian region of the Red Planet looked like a face. At least it did as long as the pixel count was small. Subsequent photos made with orbiters sporting ever-higher-resolution cameras showed it to be a large, rocky outcrop with no facial detail. This compelled the face claimers to retreat to a less tenable position: The face had been "ruined" either deliberately or by natural processes. Using this logic, every natural-looking feature on the martian landscape could be said to be truly artificial -- just ruined.

The imagery being offered as evidence of habitation on Mars is always low resolution, generally a small part of a rover image that's been helpfully enlarged by the "discoverer" so that we can better see a rock that bears an uncanny resemblance to some critter or car part.

But that's just what you'd expect if all these so-called proofs of advanced life on Mars were merely pareidolia. Take a few hundred pixels and scramble them randomly, and some will look familiar. Consider how many gazillion different animals, plants, and products exist (including, I note, even artificial rocks.) The chance that a low-res image fragment of a bumpy landscape will resemble something we've seen before is high. The chance that it proves habitation by complex life is low.

Pareidolia is a well-known phenomenon, and when its victims aren't discovering helmets and herpetologia on Mars, they will find the Virgin Mary on underpass walls, glass facades, and cheese sandwiches. I've always figured that tea leaf reading is merely a scheme for turning pareidolia into profit.

In the old days, orbital photos, with their lesser detail, could only reveal to amateur sleuths such macro-sized objects as pyramids or a giant face. Now we can see a lug nut. It's a big step forward in the search for life.