[meteorite-list] How Martian Winds Make Rocks Walk

From: Jerry Flaherty <grf2_at_meteoritecentral.com>
Date: Thu, 08 Jan 2009 21:29:04 -0500
Message-ID: <934223F4F977411EB429CEAFF5594909_at_ASUS>

Reminds me of a scietific "mystery" on one of the TV channels months ago
depicting wind driven rocks.
----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Thursday, January 08, 2009 3:28 PM
Subject: [meteorite-list] How Martian Winds Make Rocks Walk


>
>
> How Martian Winds Make Rocks Walk
> (sent by Mari N. Jensen, The University of Arizona, 520-626-9635,
> mnjensen at email.arizona.edu)
>
> -- Thursday, January 8, 2009
>
> -----------------------------------------------------------------------
> Researcher contact information is at the end of this release.
> Images: available to logged-in reporters on Eurekalert or from the
> researcher
> -----------------------------------------------------------------------
>
> Rocks on Mars are on the move, rolling into the wind and forming organized
> patterns, according to new research.
>
> The new finding counters the previous explanation of the evenly spaced
> arrangement of small rocks on Mars. That explanation suggested the rocks
> were picked up and carried downwind by extreme high-speed winds thought to
> occur on Mars in the past.
>
> Images taken by the Mars Exploration Rover Spirit show small rocks
> regularly
> spaced about 5 to 7 centimeters apart on the intercrater plains between
> Lahontan Crater and the Columbia Hills.
>
> Although Mars is a windy planet, it would be difficult for the wind to
> carry
> the small rocks, which range in size from a quarter to a softball, said
> Jon
> D. Pelletier, associate professor of geosciences at The University of
> Arizona in Tucson.
>
> Pelletier and his colleagues suggest that wind blows sand away from the
> front of the rock, creating a pit, and then deposits that sand behind the
> rock, creating a hill.
>
> The rock then rolls forward into the pit, moving into the wind, he said.
>
> As long as the wind continues to blow, the process is repeated and the
> rocks
> move forward.
>
> This explanation does not require extreme winds, Pelletier said.
>
> "You get this happening five, 10, 20 times then you start to really move
> these things around," he said. "They can move many times their diameter."
>
> The process is nearly the same with a cluster of rocks.
>
> However, with a cluster of rocks, those in the front of the group shield
> those in the middle or on the edges from the wind, Pelletier said.
>
> Because the middle and outer rocks are not directly hit by the wind, the
> wind creates pits to the sides of those rocks. Therefore, they roll to the
> side, not directly into the wind, and the cluster begins to spread out.
>
> Pelletier, Andrew L. Leier of the University of Calgary in Alberta,
> Canada,
> and James R. Steidtmann of the University of Wyoming in Laramie report
> their
> findings in the paper, "Wind-Driven Reorganization of Coarse Clasts on the
> Surface of Mars." The paper is in the January issue of the journal
> Geology.
>
> When Leier was a graduate student at the UA, he told Pelletier about an
> experiment on the upwind migration of rocks that Steidtmann, Leier's
> thesis
> advisor, had conducted.
>
> Steidtmann had studied upwind migration about 30 years ago. He used a wind
> tunnel to see how pebbles on sand moved in the wind. Steidtmann's research
> showed that the rocks moved upwind and that over time, a regular pattern
> emerged.
>
> Pelletier wasn't sure how he could use the idea.
>
> Some time later, while attending a lecture that showed pictures of
> uniformly
> organized rocks on Mars, Pelletier recalled his conversations with Leier
> about Steidtmann's experiments -- and it all came together.
>
> To investigate the regular patterns of the rocks on Mars, Pelletier
> combined
> three standard numerical computer models. The first modeled air flow, the
> second modeled erosion and deposition of sand and the third modeled the
> rocks' movement, he said.
>
> "We can model it on the computer to try to get a better sense of what's
> actually happening and to provide another sort of documentation or
> justification for the idea," he said.
>
> Pelletier was the first to combine the three standard models and apply
> them
> to this new problem.
>
> He also conducted what is known as a Monte Carlo simulation, which applies
> his combination numerical model over and over to a random pattern of rocks
> to see how the rocks ultimately end up.
>
> Pelletier ran the simulation 1,000 times. The rocks ended up into a
> regular
> pattern 90 percent of the time, he said.
>
> 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.
>
> Pelletier said upwind migration of rocks also occurs on Earth.
>
> Co-author Leier wrote in an e-mail, "Something as seemingly mundane as the
> distribution of rocks on a sandy, wind-blown surface can actually be used
> to
> tell us a lot about how wind-related processes operate on a place as
> familiar as the Earth and as alien as Mars."
>
> However, because plants and animals can alter wind patterns and rearrange
> rocks, it is much more difficult to study this process on Earth, Pelletier
> said.
>
> Of Mars' mysterious walking rocks, he said, "This is a neat problem, but
> there are bigger fish to fry."
>
> Pelletier plans to apply the same numerical models to larger features on
> Mars such as sand dunes and wind-sculpted valleys and ridges called
> "yardangs."
>
> He said understanding the climate history of other planets and where those
> climates went awry can help in understanding our own climate system.
>
> This release was written by University of Arizona NASA Space Grant Intern
> Megan Levardo.
>
> Researcher Contact Information:
> Jon D. Pelletier
> (520) 626-2126
> jdpellet at email.arizona.edu
>
>
> Related Web sites:
> Jon D. Pelletier
> http://geomorphology.geo.arizona.edu/
>
> NASA Mars Exploration Rover Mission
> http://marsrovers.nasa.gov/home/index.html
>
> # # # # #
>
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Received on Thu 08 Jan 2009 09:29:04 PM PST