The Science of Sustainability

Placing a Bet on the Surface of Mars

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Mars has been on my radar for a very long time, since the astonishing day back in 1965 when Mariner 10 first sent back a picture of craters on its surface. So I'm not a Johnny-come-lately to the red planet. I've followed the news from every Mars mission, orbiters and landers alike. But Curiosity, the most recent robot rover, has especially piqued my curiosity as a geologist. I think there are two reasons: the darn thing has finally become a decent field assistant, and NASA is sending it to some of Mars' most Earthlike places. So let me channel the late Huell Howser here and share some of what makes me go, "That's amazing!"

Unlike most previous landers, Curiosity has decent vision, about as good as my pocket camera. Its pictures actually look good on my desktop display, no longer like a frame grab from an old videocassette. Curiosity is a lot sturdier too—big, quick on its feet—and smarter.

It's got a nice hand lens, better than mine, that offers almost-microscopic closeups. It has a shovel, like lots of its predecessors did. One of my worst frustrations in watching Mars robots over the years was wishing I could lean in and just blow the dust off of things. Lo and behold, this rover packs a broom!

Mars images courtesy NASA/JPL-Caltech/MSSS

And while previous rovers had little grinding tools to function like the hammer and chisel in my field pack, Curiosity has a proper rock drill. They'll be testing it for the first time in coming weeks, somewhere in this car-sized piece of landscape named John Klein.

Until they can send a Gigapan outfit to Mars for a really huge, zoomable picture, the full-size version of this image on the NASA website at 3483 by 2651 pixels will be the state of the art.

The rocks in this part of Mars, on the floor of Gale crater, are full of minerals and features that testify to the chemical action of water. Here's a closeup from an outcrop called Sheepbed.

To all appearances it's a fine-grained sandstone, shot with veins of gypsum (like those I showed you last year) and tiny concretions of hematite, a hydrated iron oxide. Larger concretions lie in the surrounding dirt.

Elsewhere, the rover has shown us clear examples of crossbedding.

Crossbeds testify to not just the presence of water, but its physical action—rushing rivulets that sent large ripples of sand down their streambeds. Each crossbed represents the root of a ripple, spared from erosion in a setting where sediment was brought in faster than it was taken away. (Wind-blown sand dunes also make crossbeds, but the particles involved are much smaller.)

So, back to the drilling site at John Klein. I look at this detail and have several questions about it.

I see curving veins cropping out of the surface. The Curiosity team claims that "some of the veins have two walls and an eroded interior." I think they look more like double veins, but the rover will help us decide. Why are they protruding, and why is the surface around them so flat? The whole surface gives the impression of having been gently swept for a very long time—not strongly enough to streamline anything, but enough to winnow away the finest material as it works loose under Mars' 100°C daily temperature swings. What do the veins consist of, and why do they curve so tantalizingly?

Curiosity's camera is too far away to confirm or deny that curvature, and its x-ray instrument cannot yet tell us whether the veins are gypsum. So for now I can indulge in the hypothesis that we may be seeing the curving forms of liesegang structures, which you've probably noticed many times without knowing their name.

Liesegang bands in an Oakland street rock. Photo by Andrew Alden

Liesegang (LEEZ-gahng) structures are thin waves of iron-oxide minerals found in porous rocks where chemically active groundwater has come and gone. In Earth rocks they may or may not affect a stone's strength, or the difference may not matter in the abrasive environment of a riverbed, like this example. But we already know that the right minerals exist on Mars, making up the concretions. Perhaps, under the utterly different conditions of Mars, these homely features can emerge to display their thin, curving, multiple form to Curiosity's eyes and toolkit.

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Category: Astronomy, Blog, Geology

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Andrew Alden

About the Author ()

Andrew Alden earned his geology degree at the University of New Hampshire and moved back to the Bay Area to work at the U.S. Geological Survey for six years. He has written on geology for About.com since its founding in 1997. In 2007, he started the Oakland Geology blog, which won recognition as "Best of the East Bay" from the East Bay Express in 2010. In writing about geology in the Bay Area and surroundings, he hopes to share some of the useful and pleasurable insights that geologists give us—not just facts about the deep past, but an attitude that might be called the deep present. Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.
  • Graham Luell

    Thank you for your article. I'm not a geologist, and I was wondering if the curves could be the result of volcanic bubbles, and could the crossbeds be the result of some other fluid other than water?

    • Andrew Alden

      Graham, these don't appear to be volcanic rocks, so there is no possibility of bubbles (vesicles) in the rock. As I mentioned, crossbeds are also found in windblown (eolian) sediments, but the winds in Mars' thin atmosphere can only carry the finest dust. For a while, theorists were talking about liquid carbon dioxide, which could theoretically exist for brief periods, but everyone (me included) is focused exclusively on water today.

      • Graham Luell

        Ah so no volcanic vesicles, and no non-water crossbedding… how about could the curves be a fossil? What a creature that would be! (Has the rover found any signs of any possible fossils? I assume not, or we would have heard about it, but that would really be something, wouldn't it! Is it a fairly sure sign that there hasn't been life on Mars, that we haven't found any fossils yet?