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Sand Dunes On Mars In Motion

Soulskill posted more than 2 years ago | from the spice-must-flow dept.

Mars 55

TheNextCorner writes with news that NASA's Mars Reconnaissance Orbiter has detected ripples and shifts in the sand dunes on Mars, which means the surface of the planet is more dynamic than previously thought. Planetary scientist Nathan Bridges said, "Mars either has more gusts of wind than we knew about before, or the winds are capable of transporting more sand. We used to think of the sand on Mars as relatively immobile, so these new observations are changing our whole perspective." The article explains, "The air on Mars is thin, so stronger gusts of wind are needed to push a grain of sand. Wind-tunnel experiments have shown that a patch of sand would take winds of about 80 mph to move on Mars compared with only 10 mph on Earth. Measurements from the meteorology experiments on NASA's Viking landers in the 1970s and early 1980s, in addition to climate models, showed such winds should be rare on Mars."

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Nah, not wind (5, Funny)

bhcompy (1877290) | more than 2 years ago | (#38103742)

It's just the sandworms. I hope the rover that goes to the sand desert regions has a thumper

Re:Nah, not wind (4, Funny)

bosef1 (208943) | more than 2 years ago | (#38103874)

"Stilgar, have we wormsign?"

"Usul, we have wormsign the likes of which even God has never seen."

Re:Nah, not wind (0)

Anonymous Coward | more than 2 years ago | (#38108902)

Maybe the subterranean martins are into zen and come to the surface at night to rake the sands for relaxation.

Re:Nah, not wind (1)

madhi19 (1972884) | more than 2 years ago | (#38116526)

"Bless the Maker and all His Water. Bless the coming and going of Him, May His passing cleanse the world. May He keep the world for his people."

If you walk without rhythm (4, Informative)

Anonymous Coward | more than 2 years ago | (#38103756)

you won't attract the worm

Re:If you walk without rhythm (1)

masternerdguy (2468142) | more than 2 years ago | (#38103944)

But the worms have turned

Re:If you walk without rhythm (3, Funny)

BlortHorc (305555) | more than 2 years ago | (#38105432)

The spice must flow!

Re:If you walk without rhythm (1)

GregC63 (1564363) | more than 2 years ago | (#38106102)

I need melange.....

Re:If you walk without rhythm (0)

Anonymous Coward | more than 2 years ago | (#38106444)

I need three of them.

Obviously (1)

Anonymous Coward | more than 2 years ago | (#38103780)

It's obviously aliens. Gogogogo History Channel Documentary!

Local storms... (4, Interesting)

JoeMerchant (803320) | more than 2 years ago | (#38103802)

Measurements from the meteorology experiments on NASA's Viking landers in the 1970s and early 1980s, in addition to climate models, showed such winds should be rare on Mars.

Yeah, and 80+mph winds were rare in Miami in the 1970s and early 1980s too.

Re:Local storms... (1)

phayes (202222) | more than 2 years ago | (#38107284)

Nice job missing TFAs point. It's not that there are no storm systems on mars which were judged capable of high winds, it's that the dunes moved without seeing the martian equivalent of hurricanes from orbit.

On the implied subject, the sample size of huriicanes going through Miami (or just hurricanes in general) since the mid 80s is too small to support any conclusions.

Re:Local storms... (1)

JoeMerchant (803320) | more than 2 years ago | (#38107814)

Nice job missing my point. Miami is a place that experiences relatively frequent hurricanes, but if you landed a probe there and gathered data from January 1, 1970 through January 1, 1990, I don't think, in 20 years of data collection, that you would have ever witnessed a single 80+mph wind event.

Yes, they also used data gathered from orbit and other sources, but, obviously, their methods were flawed in some way - perhaps relying too much on the only two surface probes they had was a part of the problem?

As far as not seeing any hurricanes from orbit, I seem to recall periodic planetwide dust storms [nasa.gov] on Mars - did the researchers feel that these were not enough to obscure their observations?

Re:Local storms... (1)

phayes (202222) | more than 2 years ago | (#38108990)

Your point is only valid if you can statistically show that Miami has had more hurricanes than it had previously. The sample size is too small so you cannot, Not everything can be pinned on the coattails of global warming.

Now, young grasshopper try to explain how the sand dunes moved in the absence of any storms visible from orbit. The theory up to now has been. they shouldn't. They do. Do you at last understand why this is news for nerds & not just an occasion for you claim that the higher than normal temperatures in your bathtub are due to global warming?

Re:Local storms... (1)

JoeMerchant (803320) | more than 2 years ago | (#38109174)

Wow, a leap to global warming, but from where?

As for the absence of any storms visible from orbit, what's our Martian weather coverage and resolution like? Presumably, not all Martian dust storms are runaway planet-wide events.

There should be some appropriate jab at how conservatives take their own limited view of the cosmos and extrapolate it universally, all the while espousing a knowledge of statistics and sample sizes, but either being ignorant of how they really work, or more insidiously lying (to themselves more than anybody else) about how much data they have to back themselves up. I won't bother veiling it in anything remotely on-topic, just calling it how I see it, from my bathtub.

Re:Local storms... (1)

phayes (202222) | more than 2 years ago | (#38137572)

What, if not global warning, were you referring to in your first post by "Yeah, and 80+mph winds were rare in Miami in the 1970s and early 1980s too.--"?

Re:Local storms... (0)

Anonymous Coward | more than 2 years ago | (#38140950)

What, if not global warning, were you referring to in your first post by "Yeah, and 80+mph winds were rare in Miami in the 1970s and early 1980s too.--"?

I was referring to those two decades when no hurricane struck Miami, those same two decades the Viking landers were collecting weather data on Mars. A viking lander on the roof of the National Hurricane Center in Miami would not have observed a sustained 80mph wind, probably not even a gust, ever, in 20 years.

Plenty of hurricanes hit Miami in the 90s, and 60s, just not those two decades. You want theories about global warming making hurricanes stronger? They're not coming from me - check out the damage of the 1925 storm in Miami, and the 1935 storm in the Florida Keys, they're Andrew class, if not worse.

So, even though we have "decades" of ground-truth from Mars, two wind measurement stations can hardly draw conclusions about the whole planet.

Re:Local storms... (1)

phayes (202222) | more than 2 years ago | (#38147062)

much clearer, thanks.

Sands Move Everywhere (4, Insightful)

LifesABeach (234436) | more than 2 years ago | (#38103804)

When a wind storm on Mars covers a bunch of real estate, it's a easy guess that there's more than enough energy to move sand. Look any where there is sand, the stuff doesn't take much to find the inside of your shoe; go figure. Now JPL has me wondering if their next rover will be able to handle sand traversal; I guess we'll know by controlled experiment.

effects of vortexes (0)

Anonymous Coward | more than 2 years ago | (#38103850)

They are underestimating the effects of vortexes lofting higher pitched trajectories and shearing effects on the particles at those boundaries.. i think..

-g

Dunes eh? (4, Funny)

masternerdguy (2468142) | more than 2 years ago | (#38103922)

He who controls the spice...no that's too easy.

Re:Dunes eh? (1)

drinkypoo (153816) | more than 2 years ago | (#38107304)

He who controls the spice...no that's too easy.

Travel to any Dune on Mars, without moving.

Controlled for all factors? (4, Insightful)

Webs 101 (798265) | more than 2 years ago | (#38104080)

This bugs me: "Wind-tunnel experiments have shown that a patch of sand would take winds of about 80 mph to move on Mars compared with only 10 mph on Earth."

In order to move the sand, the wind must overcome friction. Sealed wind-tunnel experiments with different atmospheres can easily show that winds of low-pressure atmospheres need to have more energy to move sand than winds of higher pressure atmospheres.

But the wording of that statement doesn't mention gravity. In order to move the sand, the wind must overcome the force of friction, and of course friction depends on gravity. Did anyone adjust for Mars gravity being 38% of Earth's?

Re:Controlled for all factors? (1)

Anonymous Coward | more than 2 years ago | (#38104158)

> Did anyone adjust for Mars gravity being 38% of Earth's?

How about using less dense "sand" for the experiment?

Re:Controlled for all factors? (5, Informative)

Baloroth (2370816) | more than 2 years ago | (#38104250)

Took me about 30 seconds of computation to figure out: probably. KE=1/2 M*v^2. M(mars atm)=~.01M(earth atm). v(e)=10MPH, v(m)=80MPH. Works out (very roughly) to the same KE needed if you account for the reduced gravity. I'm certainly no fluid dynamicist though.

Re:Controlled for all factors? (1, Funny)

msauve (701917) | more than 2 years ago | (#38104310)

You could have probably saved NASA the cost of a million dollar wind tunnel experiment. Too bad they don't have anyone with a BS in physics on staff.

Re:Controlled for all factors? (1)

Baloroth (2370816) | more than 2 years ago | (#38104374)

All physics should be checked by experimental methods before being considered valid. Otherwise, all you are doing is mathematics.

Re:Controlled for all factors? (1)

msauve (701917) | more than 2 years ago | (#38104408)

So, back to the original point - how did they duplicate Martian gravity (and sand, for that matter) in a wind tunnel? I suspect they were just "doing mathematics."

Re:Controlled for all factors? (0)

Anonymous Coward | more than 2 years ago | (#38104662)

You assume they do it wrong, without every bothering to read the research. If you honestly care, look it up. I really doubt you'll find you're the smartest one.

Re:Controlled for all factors? (0)

Anonymous Coward | more than 2 years ago | (#38104818)

The claim wasn't referenced. How do you suggest he does that?

Re:Controlled for all factors? (0)

Anonymous Coward | more than 2 years ago | (#38105190)

There's this thing called a search engine which allows you to look stuff up on this decentralized planetary information depository, I've heard some people call it the World Wide Web.

Re:Controlled for all factors? (3, Interesting)

Baloroth (2370816) | more than 2 years ago | (#38106930)

Sand is pretty easy, they know the composition from probes. Gravity is a bit harder, but I'm guessing you could adjust the density of the sand to reflect the weight/ size ratio on Mars, which would give you a pretty accurate duplication of Martian conditions. Not exact, but these kinds of physics rarely are.

Re:Controlled for all factors? (2, Insightful)

Anonymous Coward | more than 2 years ago | (#38105228)

It kills me how slashdotters upvote crap post like, "Oh, did any of the PhD specialist Mars scientists remember that Mars has lower gravity than Earth??" How the hell is a dead obvious observation like that "Insightful"? Look, I can do it too: I wonder if the scientists remembered that Mars soil probably has a different composition than Earth soil. Dang I'm a fricken genius.

Re:Controlled for all factors? (4, Informative)

WillHirsch (2511496) | more than 2 years ago | (#38105914)

If anyone's actually interested in the real answer to this, the wind tunnel they used appears to be called MARSWIT [nasa.gov] and to compensate for gravitational differences they use walnut shell dust [nasa.gov] among other particles as their working soil. To fully correct for gravity all you have to do is match the ratio of the air density to the particle density. Since rock is about 5 times denser than wood but Earth air is about 20 times denser than Martian air, they don't seem to be fully compensated - but perhaps at 80 mph equivalent winds the important accelerations are all much larger than 4m/s (g on Mars) and so the difference in gravitational effects isn't that important.

Re:Controlled for all factors? (1)

llamapater (1542875) | more than 2 years ago | (#38110492)

that's a really loose approximation O.o the density is off and the friction between the particles is different. they'd get better results doing a test in one of those low gravity flights the cabins are already pressure controlled not much equipment modification to add a wind tunnel. and are they sure it's silicate sand.

The obvious is obvious (1)

dbIII (701233) | more than 2 years ago | (#38106006)

Don't you think they may have noticed that Mars is a different planet? I think it's very safe to assume that if they are going to the trouble of considering an atmosphere so thin that ice sublimes without melting that the lower gravity would also be considered - even a computer game like X-Plane goes that far.

What about gravity? (4, Interesting)

msauve (701917) | more than 2 years ago | (#38104108)

"Wind-tunnel experiments have shown that a patch of sand would take winds of about 80 mph (nearly 130 kilometers per hour) to move on Mars compared with only 10 mph (about 16 kilometers per hour) on Earth."

I can understand how they could have a low pressure wind tunnel to simulate the lower Martian atmospheric pressure, but how did they reduce the gravity by almost 2/3? There's no mention of Mars' lower gravity anywhere in the article.

Re:What about gravity? (1)

masternerdguy (2468142) | more than 2 years ago | (#38104154)

Sssh, you're spoiling the JPL illusion. Keep this up and we might actually have to send humans to Mars, which NASA would find totally unacceptable.

Re:What about gravity? (2)

LostOne (51301) | more than 2 years ago | (#38104194)

Seems to me that if you can work out the air speed needed to move sand with air of a particular density in at 1 g, you should be able to do some math to work out how that would translate at 1/3 g.

Re:What about gravity? (1)

msauve (701917) | more than 2 years ago | (#38104272)

By your logic, you should be able to do the same for the pressure difference, so why then the wind tunnel? What is the relationship between the wind speed needed to move sand around and gravity? Do you have a physical/mathematical formula to share?

Furthermore, it's known that the Mars atmosphere is dusty, so why would they think particulates just sit still? What's the particle size of the sand in those dunes? Density? They obviously weren't using Martian sand in the tests.

Re:What about gravity? (3, Interesting)

LostOne (51301) | more than 2 years ago | (#38104388)

Theoretically, you can, indeed, do the same for the pressure difference. After all, you can calculate the necessary forces to move any particular grain of sand. You can calculate various forces from the wind. You can even throw in electromagnetic effects. However, the volume of calculation makes that difficult at best. So the wind tunnel is useful, and would be a faster way to see how different air pressure, air composition, etc., affect the result. And what's to say there weren't dozens or more different experiments calibrated to measure different aspects of the problem?

And no, I don't have a specific formula to share. But I also have not conducted a detailed study (and I never claimed I did) so I do not have a detailed understanding of the dynamics in play. Still, I would expect formulas used in fluid dynamics and, get this, the formulas related to gravity, would likely apply. And given there is probably an electrostatic effect of some kind with the small particles, formulas related to electricity and magnetism might be involved.

In any event, my assertion was that it *should* be possible. I don't have any special knowledge of the problem.

Also, sure, there are suspended particulates in the Martian atmosphere. However, those are not the particles that form the dunes in the first place. The dunes would be composed of the larger (heavier) particles that need more force to move. And before you ask, I'm basing that statement on having observed drifting sand.

Finally, let me direct to you my signature, "If it works in theory, try something else in practice." I have no delusions that my "theory" is any more correct than any other.

Re:What about gravity? (1)

msauve (701917) | more than 2 years ago | (#38104508)

"However, those are not the particles that form the dunes in the first place. The dunes would be composed of the larger (heavier) particles that need more force to move."

Sure. I'd expect that the winds naturally sort by particle size. Those light enough to be kept aloft, are. Dense/large ones stay in one place. Those in between, which can only be pushed around as dunes, are. Where's the surprise in that? The surprise would be if there were a particle size distribution with a large gap between ones which could stay aloft and ones which couldn't even be moved.

Re:What about gravity? (0)

Anonymous Coward | more than 2 years ago | (#38104858)

Here's [sciencemag.org] the article in question. It's a mix of physics and math and insanely boring to me.

Re:What about gravity? (2)

dbIII (701233) | more than 2 years ago | (#38106146)

By your logic, you should be able to do the same for the pressure difference, so why then the wind tunnel?

Because while gravity is simple and easy to calculate fluid flow isn't. The only time I've ever seen an analogue computer it was sitting next to a very long pipe designed to try to get something closely resembling laminar flow, and apparently even then it was hard to get the computer model and reality to agree. Throw in a rough loose surface and you get turbulent air full of sand and that gets a lot more complicated. To solve it on a computer you've first got to work out what the computer has to do - that's the hard bit and probably only possible after collecting wind tunnel data. There is no "physical/mathematical formula to share" that's going to cover all situations and it's not trivial to work out where to start.

Re:What about gravity? (0)

Anonymous Coward | more than 2 years ago | (#38109352)

Use sand with a density of 1/3 of that on Mars?

Getting such sand to match the other properties of Martian sand could be quite a challenge, but sand varies widely in particle size distribution, particle shape, and bulk density depending on the source rock and how it was eroded.

Re:What about gravity? (1)

TheOriginalRevdoc (765542) | more than 2 years ago | (#38110994)

Simple solution: simulate the lower gravity with sand made of a material that's 2.6 times denser.

Piter (0)

Anonymous Coward | more than 2 years ago | (#38104162)

What Piter didnt mention is that we have a rover very close, veeeeeeeeery close to Duke Leto

Dunes? (1)

nege (263655) | more than 2 years ago | (#38104240)

Mars. Desert Planet. The only known source of the spice melange.

Re:Dunes? (0)

Anonymous Coward | more than 2 years ago | (#38104448)

Fortunately, the Blue Man Group can afford it.

Martion sand storms are not new news (1)

AbsoluteXyro (1048620) | more than 2 years ago | (#38106132)

If Mars has been covered in a global sand storm [spacetoday.org] as recently as 2001, why is it such a shock that there might be winds strong enough to ripple up some sand dunes?

Re:Martion sand storms are not new news (1)

phayes (202222) | more than 2 years ago | (#38107308)

The dunes moved without us seeing anything like a major sandstorm beeing seen from orbit.

How much energy would be required? (1)

dutchwhizzman (817898) | more than 2 years ago | (#38107128)

It's not about gravity, atmosphere density or any of that, but purely about the amount of energy required to move the sand. If there's enough solar energy to heat up the atmosphere, you'll get wind. If the atmosphere is less dense, it will require less energy to get winds to 80mph. that 80 mph is an arbitrary figure that shouldn't be looked upon the same as it is on earth.

Who says its wind? (2)

Hognoxious (631665) | more than 2 years ago | (#38107984)

Is Mars seismicalogically, er, seismicly, ummm, I'll come in again.

Is there such a thing as marsquakes?
 

Re:Who says its wind? (0)

Anonymous Coward | more than 2 years ago | (#38126416)

Yes, albeit less frequently and far weaker. There's more crust and a far cooler internal temperature (thus less internal motion) on Mars then on Earth.

Unrelated story (1)

ChrisMaple (607946) | more than 2 years ago | (#38113794)

Caterpillar corporation reports a great upswing in the purchase of earthmoving equipment to little green men.
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