The Martians

1. The Great Escarpment

You know that the origin of the big dichotomy between the northern lowlands and the southern cratered highlands is still a matter of dispute among areologists. It might be the result of the biggest impact of the early heavy bombardment, and the north therefore the biggest impact basin. Or it may be that tectonic forces were still roiling the early crust, and an early protocontinental craton, like Pangaea on Earth, had risen in the southern hemisphere and then hardened into place, as the smaller planet cooled faster than Earth, without any subsequent tectonic-plate breakup and drift. You would think these would be interpretations so diverse that areology would quickly devise questions that would make one or the other explanation either certain or impossible, but so far this is not the case; both explanations have attracted advocates making fully elaborated cases backing their views, and so the matter has shaped itself into one of the primary debates in areology. I myself have no opinion.

The question has ramifications for many other issues in areology, but it’s worth remembering just what the big dichotomy means for people walking across the face of Mars. Hiking across Echus Chasma to its eastern cliffs gives one perhaps the most dramatic approach to the so-called Great Escarpment dividing the two.

The floor of Echus Chasma is chaos at its most chaotic, and for someone on foot, this means endless divagations and extravagances to make one’s way forward. Nowadays one can follow the trail, and minimize the ups and downs, end runs, dead ends, and backtracking necessary to make one’s way in any direction; and the Maze Trail is the very model of route-finding efficiency through such torn terrain; nevertheless, if one wanted to get a sense of what it was like in the early days, it is perhaps better to leave the trail, and strike out to forge a new and unrepeatable cross-country ramble through the waste.

If you do that, you will quickly find that your view of your surroundings is inadequate to plan a forward course very far. Often you can see across the land only a kilometer or less. Big blocks of chunky eroded basalt and andesite are the entirety of the landscape; it’s as if one were crossing a talus whose particulates were two or three magnitudes larger than the talus one usually crushes underfoot. So that one threads through the terrain as an ant must make its way through talus. Small but unclimbable cliffs confront one everywhere one looks. The only way to make progress is to keep to ridgelines, skirting great hole after great hole, while hoping the ridgelines will connect to each other in ways that can be clambered over. It’s like negotiating a hedge maze by staying on the hedge tops.

Chaotic terrain: The name is quite accurate. Here the surface of the world once lost its support, when the aquifer below it drained rapidly away, downhill and over the horizon in a great outflow flood—in this case, down Echus Chasma, round the big bend of Kasei Vallis, down Kasei’s gorge canyon and out onto Chryse Planitia, some two thousand kilometers away. And when that happened the land came crashing down.

So you walk, or climb, or crawl, for day after day, across the tilted surfaces and broken edges of the great blocks of the fallen crust. You can see just what happened: The land dropped; it shattered; there was more of it than there was room for, and so it came to rest all atilt and acrackle. The violence of this ancient collapse has been scarcely masked by the three billion subsequent years of wind erosion and dustfall. It is an irony that such an unstable-looking landscape should actually be so ancient and unchanged.

So it is a matter of broken rock for as far as the eye can see. Which is not far, admittedly; even on the highest points along the way (the Maze Trail takes a line that runs from one of these to the next), the horizon is only three or four kilometers away. A very tight and jumbled wasteland of rust-tinted rock.

Then at the peak of one long roof beam of a ridge, you find yourself high enough that off to the east, a great distance away, just poking over the crackle, lie the tops of a mountain range, pale orange in the late-afternoon light. If you camp on this prominence, in the alpenglow the distant range looks like the side of a different world, rolling slowly up into the sky.

But the next morning you descend back into the maze of potholes and passlets, ridgelines and occasional flat block plateaus, like low rooftops in Manhattan. Crossing these terrains commands all your attention, and so you almost forget the sight of the distant mountain range, the problems are so great (it was in this region we found a providential crack in a thirty-meter cliff, which allowed us to climb down safely, lowering our packs on ropes)—until at the next prominence in your path through the chaos, it heaves back into view, closer now and seemingly taller, as one can see farther down its side. Not a mountain range, one now sees, but a cliff, extending north and south from horizon to horizon, etched in the usual spur-and-gully formation of cliffs everywhere, and somewhat saw-toothed at its top, but massively solid for all that—the etchings without any depth, like the brushing you see on certain metal surfaces.

And each day, when it stands over your horizon at all, it’s closer. It tends to stay over the horizon longer; but never all the time, as very often you drop into the depths of the next sink in this sunken land. But eventually, continuing roughly eastward, every time you are not actually in the depths of a pothole, the cliff positively looms over the world to the east, towering over the horizon, which stubbornly remains no more than five kilometers away. So at that point you have two horizons, in effect; one near and low, the other far and high.

And eventually you get so close to it that the cliff simply fills the eastern sky. It rises astonishingly near the zenith; it’s like running into the side of a bigger world. Like crawling over a dry cracked seabed to the side of a continental shelf. The gulleys and embayments in the cliff are whole landscapes in themselves now, canyon worlds of great depth and even greater steepness. Every spur between them is now seen to be a huge buttress, ribbing the side of a higher world. The occasional horizontal ledges marking the buttresses appear big enough to support complete island estates. But it’s hard to tell from below.

And indeed, by the time you reach the point called Cliff Bottom View, where you stand on one of the last high points of the chaos, nearly as high as the narrow strip of hilly plateau between the chaos and the escarpment, and you can finally see all the land between where you are and the foot of the great cliff, you can no longer see the cliff’s top. The mass of it blocks your view, and what you see rimming the sky, so far up toward the zenith, is not the true top, though it can seem so if you have not been paying attention, but is rather some prominence partway down its side.

Only by getting into a small blimp and taking off into the air, and flying up and away from the cliff, back out over the eastern part of the chaos, can you see the whole extent of it. If you keep sight of a reference mark, you can see that what down in the last camp you took for the top of the cliff was only about two-thirds of the way up it; the rest was blocked from view; and in any case the very strong optical effect of foreshortening had deceived you as to the true height of the thing. You keep floating up into the air, up and up and up, like a bird gyring on an updraft, and finally seeing all the cliff at once from this perspective, we just started to laugh, we couldn’t help it—we were laughing or crying, or both at once, our mouths were hanging open to our chests, we positively goggled at it, and there was nothing really we could say, it was so big.

2. Flatness

There are places out in Argyre that are nothing but flat sand to the horizon in every direction.

Usually the sand is blown into dunes. Any kind of dune, from very fine ripples underfoot to truly gargantuan barchan dunes. But in some areas even that is missing, and it is simply a flat plane of sand or bedrock, with the sky arching over it.

They say that if you look at it closely, the sky forms the visual equivalent of a dome overhead. Not a true hemisphere, but flattened somewhat. This is a virtually universal human perception, the result of consistent overestimation of horizontal distance compared with vertical distance. On Earth the horizon seems to be two to four times farther off than the zenith overhead, and if you ask someone to divide the arc between the zenith and the horizon evenly, the point chosen averages well less than forty-five degrees; about twenty-two degrees by day, I have found, and thirty by night. Redness increases this effect. If you look at the sky through red glass it appears flatter; if through blue glass, taller.

On Mars the unobstructed horizon is only about half as far away as it is on Earth—about five kilometers—and sometimes this simply makes the zenith seem even lower—perhaps two kilometers high. It depends on the clarity of the air, which of course varies a great deal: Sometimes I have seen the dome of the sky appear ten kilometers high, or even transparent to infinity. Mostly lower than that. In fact the vault of the sky is a different shape every day, if you will take the time to look at it carefully.

But no matter the transparency of the sky, or the shape of the dome it makes overhead: The sand is always the same. Flat; reddish brown; redder out toward the horizon. The characteristic redness occurs if even one percent of the bedrock or the dust on the ground is made up of iron oxides such as magnetite. This condition obtains everywhere on Mars, except for the lava plains of Syrtis, which when blown free of dust are nearly black—one of my favorite places (also the first feature to be seen from Earth through telescopes, by Christiaan Huygens in 1654).

In any case: a perfect red plane in all directions, to the round horizon. Inside certain flat craters, you stand at the center and see a double horizon, in fact: the lower one five kilometers away, and perfectly straight; the higher one farther away, and usually less straight, even serrated. (This second horizon also considerably flattens the dome of the sky.)

But the completely flat areas are the purest view. Much of Vastitas Borealis is so flat that only millions of years of existence as the floor of an ocean can explain it. And parts of Argyre Planitia are equally flat. We cannot lose these places. In these regions one stands confronted by a radically simplified landscape. It is a surreal experience to look around oneself—surreal in the literal sense of the word, in that one seems to stand in a place “over-real,” or “more than real”—a higher state than reality; or reality revealed in its barest, most heraldic simplicity. The world says then, This is what the cosmos consists of; rock, sky, sun, life (that’s you). What a massive aesthetic impact is conveyed by this so-simplified landscape! It forces you to pay attention to it; it is so remarkable you keep looking at it, you cannot do or think anything else—as if living in a perpetual total eclipse, or within any other physical miracle. Which of course is always the case. Remember.