Not everything in the solar system is as solid as it looks at first glance. Take Phobos, the larger moon that orbits Mars. It looks solid, but it may well be an orbiting pile of rubble. Now where would that rubble come from? Most likely a collision of some kind.
The European Space Agency’s Mars Express mission passed by Phobos this past summer and took a series of high-definition stereo images and data. That information got fed into a 3D modeling program that is letting astronomers measure this moon’s characteristics, including its volume and the interacting gravitational tugs between Mars and Phobos.
The analysis suggests that Phobos may be more of an asteroid than a body that evolved as a single piece.
The closest match that scientists can make for Phobos is with D-class asteroids, which are highly fractured and riddled with caverns. They are really more like pieces of rock that stick together by gravity. Scientists refer to these loosely grouped rock piles as “rubble piles.”
So, if it’s likely that Phobos didn’t form around Mars, how did this orbiting rocky junkyard get into its current equatorial orbit around Mars? There are two ideas. First, Mars gravitationally “captured” a passing rubble pile, which settled into orbit as Phobos. Deimos, the other moon, was likely captured the same way.
Phobos: an orbiting rubble collection?
The other possibility is that a meteorite (a chunk of rock from an asteroid) smashed into early Mars and pieces of it got blasted back into space. Eventually, they clumped together into a rubble pile of rocks bound together by gravity, forming what we know today as Phobos.
In the near future the Russian space agency will send a probe called Grunt to Phobos to do study this moon and collect samples of rock for further study. Studies of rocks and continuing studies of Phobos’s subsurface structure (done using radars onboard the Mars Express spacecraft) will help astronomers figure out at least some of Phobos’s past and possibly even its origin.
Take a look at this picture and tell me what you see.
Yep, it’s from the surface of Mars, in an area called Cydonia. A pretty famous section of Mars in some eyes. To a geologist, and anybody who has ever looked at rocks and formations while taking a hike through a desert or the mountains, it’s a plain with a lot of eroded rock formations on it, some craters, and maybe some ground cracks and areas where lava may have pooled once. If you go to the Mars Express web page for its current Mars exploration, you can click on any number of images of this region in high-res and in 3D restoration. It’s a fascinating area, full of geological clues for a region that is characterized by wide debris-filled valleys and full of little mounds like you see here. Many of these knobs and mounds are made of layers of rock that are more resistant to erosion than the surrounding plains rocks. So, when erosional forces (possibly flowing water) took away the more easily removed materials, they left behind this little plain of mounds.
As on Earth, if you look at an eroded knob of rock under certain conditions, it might look like something else — an animal, a head, a hand, a face. Earth’s surface is full of places like that. The most famous in my neck of the woods fell down a few years ago, but people still talk about the Old Man of the Mountain at Franconia Notch in New Hampshire. Nobody ever suggested it was man-made; everybody pretty much understood that the elements had eroded the rock away to make the head-shaped protrusion. The elements proved too much, and a few years ago the head collapsed and the Old Man was gone.
Much the same thing is happening now with our understanding of the knobs of Cydonia. Any geologist worth his or her salt could look at those knobs and understand what formed them. I think planetary scientists are still trying to decide when the floods that made these knobs occurred, and why. But that’s a scientific argument that can be resolved with more study of the area and better understanding of the geologic past of the planet.
However, at least one of those knobs has made a lot of money for several people whose use and abuse of science in the name of publicity and ego-bosting has led to a faux controversy about what the knob is. Here’s how it happened. In the 1970s, Viking Mars orbiter images (low-res and not very good) showed what looked like a face in Cydonia. It was pretty much understood that this was a case of pareidolia, the tendency of people to see things that aren’t really there in a pattern of light and shadow. It’s the sensory misperception that lets people see images of prophets on tortillas and old men in a crag of rocks. Anyway, that picture (which you can see on the ESA web site) started a cottage industry of feverishly imaginative people who have been making money and publicity for themselves ever since, claiming one eroded mesa on Mars was somehow a face carved out by ancient Martians (for which there’s NO proof) millions of years ago to send a message to people on Earth (who, depending on who you believe about when this rock was carved, probably didn’t exist yet).
That’s quite an achievement for life forms for whom there’s no proof of existence despite nearly 30 years of on-planet and orbiting exploration of Mars. That being said, I guess there probably IS intelligent life behind the stories of a face on Mars, but it’s an intelligence that isn’t being used very well, and twisting perfectly good science around to suit a singularly selfish purpose.
But, you may ask, aren’t there controversies about what happened on Mars? Absolutely. But they are all based in the science we get from our spacecraft, science we can check out with similar rocks and materials here on Earth. Geology is a very mature science, and as its precepts are applied to what we find on Mars, we are learning more about a thoroughly fascinating planet. Mars is so interesting, in fact, that we don’t need fairy tales about ancient Martians to stir up interest. And when the first folks step onto the surface of Mars sometime in the next few decades, I hope that Cydonia is one of the places they visit early in the mission. I’d love to know just how torn up the place is from the ancient floods that sent rocks tumbling across a flood plain. And, a few rock samples would tell us more about the history of water on Mars than any stories about crystal temples and benevolent beings conjured out of thin air. You see, real science is pretty darned interesting on its own!
