Curiosity Mars rover to investigate classic rock type

Nasa's Curiosity rover will soon return to a spectacular set of rocks on Mars to confirm their deposition in water billions of years ago.

Shaler outcrop on Mars

The Shaler outcrop pictured with Mount Sharp in the distance. This panorama was built from pictures taken by the rover's navigation cameras, and assembled by Ken Kremer and Marco Di Lorezo. (


Things have been a bit quiet on Mars of late. During most of April, Nasa's Curiosity rover enjoyed some R&R while the Red Planet moved behind the Sun as viewed from Earth.

This conjunction, as it is known, plays havoc with communications and the robot was forced to park up while the celestial mechanics took their course. But the ability to send commands has now been restored, and scientists have a heavy schedule of tasks they want the rover to work through.

The vehicle is currently sitting in a small depression on the floor of Gale Crater known as Yellowknife Bay. Just before conjunction, it drilled into a mudstone in a rock unit referred to as Sheepbed and found further compelling evidence for a watery past in Gale - sediments that possibly once formed a lakebed.

Curiosity is due to turn its drill again in this mudstone for further analysis before climbing out of Yellowknife Bay and heading for the crater's big central mountain, Aeolis Mons (Mount Sharp).

But almost as soon as it starts that journey, the robot is going to stop at some of the most spectacular rocks seen so far on the mission.

Scientists have mentioned the so-called Shaler outcrop but haven't yet spoken about it in great detail.

Shaler is a classic example of cross-stratification - a structure produced from thin, inclined layers of sediment.

Start Quote

You could use the Shaler pictures of cross-bedding in an intro-textbook”

End Quote Prof John Grotzinger Curiosity Project Scientist

You'll have seen examples in a river or on a beach.

The turbulent flow of water creates undulations in the bed sediments - a series of ripples or dunes that slowly migrate in the direction of the water current.

The sediment grains bouncing along the bed get pushed up the rearward-facing slope (stoss) and then avalanche down the other side (lee).

As they cascade downwards, they form discrete layers that can be preserved over geological time as laminations in the rock.

If you look at the pictures of Shaler taken by Curiosity, you can see how subsequent erosion has taken its toll on this preserved bedform. Layers just a few millimetres thick are now falling out. Thin plates of rock are strewn over the ground.

For anyone about to begin their study of geology, cross-stratification, or cross-bedding, will be one of the first topics to be covered in "sedimentary processes", and Shaler is a beautiful example.

"It's textbook; you could use the Shaler pictures of cross-bedding in an intro-textbook," Prof John Grotzinger, the project scientist on the Curiosity mission, told me.

"For a while Shaler really was a contender to drill. We were discussing it as a team and then we drove down into Sheepbed and thought 'wow, well let's put Shaler off to the side'."

Cross stratification Sedimentary processes at work on Earth are also seen in play on the Red Planet

But scientists will now get a chance to study Shaler in more detail in the coming weeks, using the rover's cameras and survey instruments.

They're keen to establish for sure how those thin layers were built.

At first glance, it might seem obvious that it was through the action of flowing water (fluvial), but the Curiosity team needs to rule out the possibility that these rocks were deposited by the wind (aeolian) or by some kind of surge, such as the fast-moving clouds of gas and rock that will often plummet down the sides of particular types of volcano (a pyroclastic surge).

"Aeolian. That's the one you always have to falsify on Mars because it's a windy planet," says Prof Grotzinger.

This can be done by looking at the size of the rock grains in the layers; and from the pictures taken of Shaler on the way into Yellowknife Bay, it seems the particles are simply too big to have been carried in the wind. Further imagery will confirm that.

Start Quote

What you're recording at Shaler is perhaps just a few minutes to hours of migration in those dunes, and then that activity has been preserved for billions of years”

End Quote Prof Sanjeev Gupta Imperial College London

There are ways to discount the base surge idea, also, explains Dr Lauren Edgar from Arizona State University.

"If you're migrating faster than you're accumulating, you just preserve the lee side because you're eroding on that stoss side. However, in a pyroclastic surge environment, you often have high rates of accumulation relative to migration, so as the bedform is migrating it is also rapidly accumulating more sediment. This means you tend to get the full stoss-side and lee-side preserved," she told BBC News.

Another check is to look for a diversity of flow directions. A surge deposition will tend to move radially away from a point source. Cross-stratification from water currents, on the other hand, will likely show movement in assorted directions.

To be honest, it's hard to think where a surge might have come from in Gale. There are no volcanoes around.

But Curiosity should nail all this with its return visit to Shaler.

Here's the really clever thing, though, I think. Cross-stratification is one of those rock structures that is so well understood, you can use it to pull out some amazing information about the past environment in which it occurred.

I've mentioned the direction of flow, but you can also determine the depth of the water and the speed of the water - not precisely, but to a good approximation.

Take a trip to Mars

Mars Rover

Ponder that for a moment. That's information about an environment that existed on another planet millions of kilometres away.

"The other really nice thing," says Prof Sanjeev Gupta, a Curiosity science team-member from Imperial College London, "is that what you're recording at Shaler is perhaps just a few minutes to hours of migration in those dunes, and then that activity has been preserved for billions of years. That's stunning."

Edgar, Grotzinger and Gupta presented their latest thinking about Shaler on a poster at the recent European Geosciences Union General Assembly. Two of their colleagues on the work have some particularly nice web resources related to cross-stratification.

Prof Dawn Sumner from the University of California at Davis describes how the layers are built in a YouTube video. Dr Dave Rubin, at the US Geological Survey, has a collection of animations to show the different forms. And click here to see a tank experiment. Watch the ripples migrate into view from the left.

Finally, listen out for Sanjeev Gupta on the BBC's The Life Scientific next week. He'll be talking about Mars with Jim Al-Khalili.

Gale map After landing on the floor of Gale Crater last August, Curiosity drove east. It passed Shaler on its way into Yellowknife Bay. When the rover drives back out in the coming weeks, it will stop at Shaler for a closer look
Jonathan Amos Article written by Jonathan Amos Jonathan Amos Science correspondent

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  • rate this

    Comment number 138.

    "The question is what happened to life on mars, to the martians why didn't the "evolve", does this contradict theory of evolution?"

    While water may be necessary for life, or at least life as we know it, that does not mean wherever there is water there must also have been life! As yet there is no evidence there ever any life on Mars to have evolved (or even been 'created', come to that).

  • rate this

    Comment number 137.

    That Mars contained water in the past has become trivial and common knowledge. The question is what happened to life on mars, to the martians why didn't the "evolve", does this contradict theory of evolution? The next step should be to dig deep into mars and search of subterranean martian. Legend has it that even in Earth there are subterranean peoples who live underground to afraid to come out.

  • rate this

    Comment number 136.

    Desperately tried to 'like' comment 127, and now it seems that I have accidentally demoted it by one 'like'

    Is 41 too old for an iPad?

    Are the BBC able to right this terrible wrong?

  • Comment number 135.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 134.

    This seems like far too simplistic an explanation.

    I suspect that the black areas may be covering;

    A. Martians
    B. Russians
    C. Berlusconi's legal team.

    Any other ideas?

  • Comment number 133.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 132.


    The whole images is compiled from a series of smaller images, the black areas are the spaces that they do not have images for. There is no conspiracy here

  • rate this

    Comment number 131.

    What is all this nit-picking and squabbling amongst yourselves? Have any of you worked for NASA? Were you there?

    I hope that NASA will soon have the technology and facilities ready to send all you trolls to Gale Crater next.

  • rate this

    Comment number 130.

    I'm more interested to know what could possibly be behind the black elements of this photograph.... Something they don't want us to see perhaps? It seems that no one else here has commented on that either....

  • rate this

    Comment number 129.

    "any explanation for life needs to account for ZERO planets with life sufficiently advanced to initiate contact wtih us."

    Oh, it's all about us, isn't it?

    Anyway, here's one: they picked up the early transmissions of Coronation Street and concluded that we're not worth contacting (quite rightly).

  • rate this

    Comment number 128.

    Re 125 PI
    I wouldn't consider myself to be a 'victim' of anything, any more than I guess that you would consider yourself a 'victim' of some kind of anthropocentric teleology. We have different world views which is fine with me, but it still doesn't get round my point that the Big Bang theory doesn't require a universe teeming with life, only the life required to propound the theory...

  • rate this

    Comment number 127.

    As a 70-year-old newcomer to BBC forums, I am beginning to see why most of my friends and acquaintances - mostly intelligent and well-educated people, scientists and otherwise - refuse to touch it with a bargepole. A triumph of science, engineering and human ingenuity such as Curiosity deserves better than a playground-level trading of insults.

  • rate this

    Comment number 126.

    if it doesn't find anything interesting soon, I shall be withdrawing my application for the one way trip.

  • rate this

    Comment number 125.

    23, as others have noted, the UK is on the new lander, along with serious contributions on many others. On Titan, a largely UK designed and built probe sits on the surface, deployed from NASA's Cassini probe in early 2005. The most distant landfall of a man made object that will likely remain so for the rest of out lives.

  • rate this

    Comment number 124.

    Re 122.NeilSkye
    No life is not a minor detail; you are a victim of the assumptions of Scientific Materialism. Life is the meaning and purpose of the universe with material being the scaffolding on which life is 'hung'. Have a baby and look into his or her eyes: feel the connection and you will get it.

  • rate this

    Comment number 123.

    After reading through all of these comments, I am struck by one outstanding mystery.
    Why does the BBC not have a progressively indented "reply to" system?

  • rate this

    Comment number 122.

    re115 PI
    Category error. The Big Bang theory isn't "an explanation for life" it's an explanation for the universe in it's entirety. Life as we understand it may be ubiquitous or a local anomaly but that's a minor detail...

  • rate this

    Comment number 121.

    119.And_here_we_go_again Your good at putting words into people’s mouths to suit your agenda. Where have I devalued scientific research?
    I raised concerns as to a 'base level' of knowledge. A level that wouldn't detract from specific research but without could blinker other applications/advancements! I'm sorry any scientist who can't wire a plug needs to have a quiet word with themselves!

  • rate this

    Comment number 120.

    Excellent article, though I can't help inferring from the headline that NASA is committing funds to research the kind of people who listen to "Stairway to Heaven" and "Free Bird" all the time :-)

  • rate this

    Comment number 119.

    What specific advancements do you see as missed?

    The thing with many people who get heavily involved in research is that they tend to have a very focused mind, especially in science, thus having huge knowledge on subjects that interest them and limited outside. The fact an expert in string theory can not wire a plug does not make their work less valuable.


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