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The Jumping Rocks of Mars

The views expressed are those of the author and are not necessarily those of Scientific American.

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Now you don’t see it, now you do.

Ten years into a mission that was originally going to only last a few months, NASA’s Opportunity rover continues to turn up surprises on Mars. In this case quite literally. Take a look at the following pair of images from the rover’s location at ‘Solander Point’, up on the rim of Endeavor Crater.

Before...and after (Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.)

See anything different between them?

Yep, 12 sols (martian days) later there’s a bright looking rock sitting on the surface that wasn’t there the first time Opportunity looked.

What is it? Did some sneaky martian creep up and put it there to flummox us?

Probably not. But the appearance of this pebble, now named ‘Pinnacle Island’ (it’s only about the size of a small clenched fist, or jelly donut as the rover scientists described it), is certainly surprising given the usually desolate and static nature of the landscape. Since the rover did not drive directly over this location, there are two plausible theories. The first is that there was a nearby meteor strike and this rock was lofted into the air to land here. The second is that the rover itself, now somewhat clumsy as motors on its wheels have degraded and failed, churned up and ‘tiddlywinked’ the rock a meter or so from its original spot.

Close up of the rock (Credit: NASA/JPL-Caltech/Cornell/Arizona Univ.)








This second explanation seems most likely. Since the rover is the only mobile entity on this bit of Mars (Curiosity being a long ways away) the simplest explanation is almost certainly the correct one.

It may also turn out to be a wonderfully serendipitous bit of environmental damage – the rock has a high sulfur, magnesium, and manganese content, placing into a new category compared to previous mineral sightings. It looks like we’re seeing the underside of material that was, until 12 days earlier, snugly buried in the martian regolith and therefore unexposed to the atmosphere and weather.

But could the rover have really kicked a rock out like this? It’s important to remember that the surface gravity on Mars is about 38% that on Earth. That means that if something is thrown it will spend about 2.6 times longer aloft than an equivalent throw on Earth (equivalent in the sense of the same velocity vector, and ignoring drag). It will therefore travel horizontally 2.6 times further than it would on Earth.

We tend to forget about this kind of simple physics, and can probably thank Hollywood for that. I’ve yet to see a fictional movie about Mars that properly imagines the basic mechanics of being in 0.38 g’s. The fact is that stuff on Mars is going to be a lot more readily dispersed and thrown around than we’re used to, and Opportunity itself is indeed the likeliest culprit for this sudden rock appearance.

Nonetheless, such attention to what is, let’s face it, a rock, does also bring to mind a marvelous TED talk parody by The Onion.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. David Cummings 7:42 pm 01/22/2014

    Opportunity has earned a spot on the cover of the Rolling Stone.

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  2. 2. cheeverwoodlot 8:53 pm 01/22/2014

    It seems rather evident that the rover didn’t move a discernible distance in the time period between the 2 photos. That being the case, I find it difficult to understand how the rock was “churned up” by the rover, lesser Martian gravity notwithstanding. It’s also hard for me to understand how a rock churned up from the surface would have such a “clean”, i.e. freshly-fractured appearance.

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  3. 3. MadhavaVermaDantuluri 11:13 pm 01/22/2014

    still, some hope and we are getting new information.

    Link to this
  4. 4. stargene 11:31 pm 01/22/2014

    Here’s a thought. It may be possible, at least in
    principle, to distinguish the two hypotheses.

    Using special computer processing, take a number
    of detailed shots of the rock and its surrounds.
    Then examine in detail which others rocks and
    grains may have been dislodged by that rock in
    its original trajectory, either from the rover’s
    wheels or from some non-rover direction. This
    could possibly track the new rock’s original
    bouncing path. A good computer program should
    find this relatively easy to do.

    Link to this
  5. 5. ChristineFulks 4:11 am 01/23/2014

    what Christine responded I didnt know that some one can earn $4837 in one month on the computer . take a look at the site here>>>> T­E­C­8­­0.C­O­M

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  6. 6. carboncosm 11:45 am 01/23/2014

    If at all feasible, they ought to see if they can overturn Pinnacle Island rock to confirm its appearance before it got flicked to its new position, then attempt to pry up and turn over another small rock of similar appearance to see if similar materials are present. Unfortunately, the rover is limited in its manipulative abilities, a puzzlingly persistent engineering oversight when it comes to Mars rover design. A good field geologist can at least pick up rocks and turn them over.

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  7. 7. singing flea 2:55 pm 01/23/2014

    The natives in Hawaii believed rocks were alive. They believed all things had mana or life. After living on a rocky volcano (Mauna Loa)for the past 20 years I can certainly see why they believed this. I am constantly moving rocks off my driveway and the roads here because they do indeed move all the time. Its a result of erosion, wind and even earth quakes which frequent the mountain. I would like to see the surrounding area to see if it could have shifted from a higher place.

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