Rock-Walkin’ on Mars

It’s all in the Wind Action

Five years of rover studies on Mars have uncovered some cool sights on the Red Planet. Through their eyes we’ve seen the planet change in subtle and not-so-subtle ways, and examined the tiniest details allowed by the resolution of the rover instruments. This is important in planetary studies. Sure the  big pictures are important, but the true history of a planet lies in its day-to-day, minute-by-minute changes across small areas of the surface.

These Spirit Rover camera images of an intercrater plain between Mars Lohontan Crater show uniformly-spaced small rocks called clasts. Courtesy Geological Society of America.
These Spirit Rover camera images of an intercrater plain between Mars' Lohontan Crater show uniformly-spaced small rocks called clasts. Courtesy Geological Society of America.

So it goes with the distribution of rocks across the planet’s surface. It may surprise you to know that rocks on Mars are walking across the surface, with the help of the ever-present Martian winds.

If you examine the images of rocks strewn across an intercrater plain studied by the Mars Spirit rover, you can see that they are pretty much evenly scattered, suggesting that something — a mechanism like wind action — has acted to distribute them in regular spacing — about 5 to 7 centimeters (a few inches) part —  as you see them here.

At first, scientists thought that perhaps high-speed winds in the past might have somehow tumbled these rocks into place. But, new research shows that it would be difficult for winds to carry these small rocks — which range from quarter-sized chunks to softball-sized blocks — very far.   Jon D. Pelletier (associate professor of geosciences as the University of Arizona in Tucson) and his colleagues looked at images of such rock plains taken by the Spirit rover and came up with an alternate mechanism for “rock walking” that makes more sense.

They suggest that the Martian wind blows sand away from in front of  a rock, which creates a small pit. The sand whirls around and ends up behind the rock, forming a sort sheltering wall.  Eventually the rock rolls forward into the pit, actually moving into the wind. As the wind continues to blow, the process gets repeated and the rocks make their way across the surface, tacking into the wind centimeter by centimeter.

Clusters of rocks go through the same process with almost similar results. The difference is that the forward “wave” of rocks in the cluster shelter those in the middle or the sides from the wind.  The sheltered rocks aren’t hit directly by the wind and the pits that are created lie to the sides, not the front. So, when those rocks start moving, they fall sideways. Over time the side-winding motion scatters the rocks out across a wider area.

These images show how simulated rocks end up being spaced by simulated winds like thos eon Mars. The image on the left is the starting position of the rocks; the image on the right shows where they end up after being affected by the wind. The yellow streaks represent the sand piled behind the rocks by the wind. Courtesy Jon D. Pelletier, University of Arizona.
These images show how simulated rocks end up being spaced by simulated winds like thos eon Mars. The image on the left is the starting position of the rocks; the image on the right shows where they end up after being affected by the wind. The yellow streaks represent the sand piled behind the rocks by the wind. Courtesy Jon D. Pelletier, University of Arizona.

How did Pelletier figure this out? He constructed a computer simulation of Martian winds acting on rocks and sand.

He ran the simulation a thousand times, and 90 percent of the time the rocks ended up in a regular pattern.

As an independent verification, he also compared the pattern predicted by the numerical model to the distances between each rock and its nearest neighbor in the Mars images. The patterns of the Martian rocks matched what the model predicted.

Now, this upwind migration doesn’t just happen on Mars. Geologists also see it happening on Earth.

Pelletier’s colleague and co-author Andrew Leier pointed out that this mundane distribution of rocks on a sandy, wind-blown surface can actually tell a lot about how wind-related processes operate on a place as familiar as the Earth and as alien as Mars.  On Earth, the process is complicated by life because plants and animals can alter wind patterns and rearrange rocks, which actually makes it tougher to study here than on Mars.

Next up after the rock-walking study for Pelletier is to apply this same technique to larger wind-blown features on Mars.  So, in the near future, look for a deeper understanding of the motions of sand dunes, wind-sculpted valleys and ridges (referred to by geologists as “yardangs”).

Studies such as Pelletier’s are small steps toward a deeper understanding of the climate history of other planets and particularly where those climates where those climates went awry. Such information tells us much about those planets — and about our own planet and its climate, too.

Nobody Knows!!! WOOOO!!!!!!

Breathless Hyperbole and Critical Thinking

More than a week ago humans stood on the cusp of change. We were rapidly coming to the end of the Year-count — a calendrical numbering system derived from ancient counting methods first devised by the Egyptians, refined by the Romans, and revised into today’s form through a set of mysterious-seeming changes instituted by Pope Gregory XIII.

In short, we were rapidly approaching a change-over.  As the last days of December ticked away, we were all faced with the knowledge that a cycle of time was coming to an end.  There wasn’t a lot of information available to us about what would happen after that cycle ended. Nobody knew what would happen when 2009 finally arrived. There was zero scientific evidence that anything WOULD happen, but there were numerous things that could easily threaten humans in the new year.  Things like war.  Peace.  Asteroid sightings. Financial ruin. Political changes.  Medical issues.  Pestilence.

And all these things could be connected back to this mysterious changeover of time from one year to the next.

Worried yet?  No?

Good for you.  You probably recognized that I was talking about the the New Year, when we ticked over from 11:59:59 31 December 2008 to 12:00:00 1 January 2009.  At that moment, the very human-based method of timekeeping that we call the Gregorian Calendar, ticked over from one year to the next. And with it, life on Earth stepped forward one more instant into the future.  We are a time-based species and each second is a step into the future. No second is any more special than the next in the grand scheme of things.  We keep breathing, eating, sleeping, working, making war, making peace, doing things. The planet keeps going around the Sun. The Sun keeps moving through the galaxy, and the galaxy keeps spinning around.

There’s nothing mysterious about any of this because it’s all part of our existence — time flows forward and things happen.

Cum hoc ergo propter hoc (or, Correlation Does Not Imply Causation)

You may have noticed a certain breathless hyperbole about the coming year 2012. This is a time when, according to a widely varying number of woo-woo “historians,” overeager New Agers, and folks who have books they want to sell are telling everybody that somehow something is going to happen that will affect all of mankind.  This is pretty standard woo stuff; amusing to read and usually having little basis in logical thought. It speaks to a human propensity to attach meaning to things that are usually unrelated in an effort to tell a good story. There’s nothing wrong with good storytelling, but there’s an unsubtle difference between doing so and coming up with wild theories that sorta kinda sound scientific and attaching them to distinctly odd metaphysical weirdness.

Anyway, this latest spate of delusional storytelling is based on the Maya Long Count, which is simply a calendar that the ancient Maya came up with to count time. It’s a calendar, not a prediction device. It doesn’t have weird powers or require that you have a doctorate to understand that it measures time just like the calendar in your kitchen does.

However, some folks saw that the Long Count is coming to an end in 2012 and attached meaning to things that they think will happen at that time as evidence that the Long Count is somehow connected (or even causing) these events.  Some of the events are simply made up; others (like climate changes and political events) are going to happen no matter what, but they make a good story when connected to the 2012 “tick-over” of the Long Count.

Like every other calendar, the Long Count has an end date, and like every other calendar, it expects to tick over to a new period of time. It’s as simple as going from 1:59:59 31 December 2008 ticked to 12:00:00 1 January 2009.  I’d like to point out that on New Year’s Day, we all flipped over our calendars and proceeded along with our lives as we always do.

There’s an excellent quote on the Wikipedia article about the Maya calendar and the end of the Long Count that I will share with you here:

“”For the ancient Maya, it was a huge celebration to make it to the end of a whole cycle,” says Sandra Noble, executive director of the Foundation for the Advancement of Meso-American Studies, Inc. in Crystal River, Florida. To render December 21, 2012, as a doomsday or moment of cosmic shifting, she says, is “a complete fabrication and a chance for a lot of people to cash in.”

Of course, there are all kinds of web sites out there that are taking this Long Count business WAY outside of the realm of logic and critical thinking. They are promulgating things like mysterious galaxy-wide metaphysical beams that will somehow bring along a new age of enlightenment or something. One of my favorite sites for this Woo-vian blah-blah even goes so far as to say “Nobody knows what will happen!”  And then goes on to imagine the most amazing spun fantasies that seem kinda, sorta scientific if you don’t look too closely.

We’ll probably be hearing more about all this nonsense over the coming years. Hollywood has weighed in with some silly movie about researchers fighting off volcanic eruptions and typhoons for 2012.  Of course, volcanoes erupt every year, and typhoons are a yearly occurrence so, I’m not sure why they’d take on more meaning in 2012. But hey, I’m not woo, either.  Anyway, based on hard evidence from other movies I’ve seen that take on science (and science loses nearly every time), I predict that the science in the 2012 movie will suck and the critical thinking factor will be just about zero. I just keep telling myself, “It’s only a movie… ”

Anyway, for your edification, I submit Ian O’Neill’s lovely posting about the 2012 “enigma” here.  He does a good job debunking this whole 2012 thing.  And, while you’re at it, go read here about the Maya calendar. If you’re interested in learning more about Mesoamerican cultures and astronomy, I suggest you pick up Ed Krupp’s SkyWatchers, Shamans, & Kings. his Echoes of the Skies, or Tony Aveni’s Stairways to the Stars: Skywatching in Three Great Ancient Cultures.