Martian dune dynamics Options

[Arizona Dave]

It an ok video, but I must point out at saying that Mars Atmosphere is Less that 1% as "Thick" as Earth's" is both incorrect and misleading, its supposedly less than 1% as Dense...im sure this will rub a few ppl the wrong way, but in science terminology is very important. (there is debate and precedence for dust blocking tubes in all pressure sensors used to date, and the Arm that was designed to measure wind speeds broken upon impact on Curi - and dust devils based on rotation havnt presented speeds over about 50-55 mph...less than half the minimum AIMS needed to replicate them in their near-vacuum experiment -- another discussion I know)

Thick vs Dense - Not only does they way one describe something give other's important information about that something, using wrong terms can drastically change the meaning of something, leading others to design things incorrectly, and/or perpetuate incorrect information. Articulate and Precise communication is important, and especially so when presenting things for the public sphere - whether or not the average person knows thick vs dense, many do, and someone unfamiliar with previous data sets and facts could very well take the "thick" to mean distance extending up from the surface, or even some other way...in other words, regardless of who the audience is..clarity and correctness should prevail, of for no other reason than to be able to always say "We said X, and it meant X, not Y"

The fact that these dunes have large and small grains at the surface that migrate, is empirical proof that some force is moving them. We know the sizes of the grains, we know the composition of much of the minerals, and thus the density and weight of the grains, we know Mar's gravity, and using all those data sets, we can then calculate what force it takes to move grains...that amount of force then tells us what force of wind it takes to move them...which all leads back to atmospheric density, not how thick the atmosphere is.

The distance these dunes (and others) move per MOC and HiRise images contradicts known wind speeds vs *observed* Atm pressures...so something is off, or some other forces assist (static elect, CO2 out gassing, Water Vapor suspension?), and Im hoping they can really study these things to figure out why and how things are observed moving in atmospheric pressures that would suggest only the finest of particles could be moved.

Im also very intrigued by the colors seen in these latest images and all the different mineral types being seen in close-ups.

Mars keeps throwing curve balls.

[mcaplinger]

The distance these dunes (and others) move per MOC and HiRise images contradicts known wind speeds vs *observed* Atm pressures...so something is off...

Uh, no. See http://www.mars.asu.edu/christensen/docs/e...unes_JGR_91.pdf

[Arizona Dave]

Uh, no. See http://www.mars.asu.edu/christensen/docs/e...unes_JGR_91.pdf

Interesting that the report is from 1991...before we had close-up images of actual dunes and thus particle sizes, and before we had more wind data.

Looking at the latest Curi Images, one might be prudent to reconsider that these dunes are of the same particle size, porosity, and mineralogical make-up that this 1991 report assumed...

I also think its funny that they consider images taken from orbit from 1981 as "Very High Resolution".

In any event, here is this: http://www.nasa.gov/centers/ames/research/...cumchamber.html

AMES had to use air speeds of "230 feet per second" (thats 156.8mph), and "Dust on Mars is extremely fine, being about the size of flour used in baking bread," Greeley said. For simulated Mars dust, researchers often use 'Carbondale red clay,' because it is less than 0.0000787 of an inch (two microns, or 2 millionths of a meter) in size." in order to get the dust devils to form.

They further went on to explain that "There is a difference between Mars wind blowing dust, and 'dust devils' lifting dust. Like a vacuum cleaner, a dust devil has lower pressure in its core, which means that it is easier for dust devils to put dust particles in motion than for wind to do so."

Which is saying "Dust Devils can move the fine particles easier than just blowing wind"...

Yet wind speeds have only been measured up to around 58 mph...or about 1/4th the AMES speed it took to lift particles.

I have worked with vacuum chambers before, once your down to the 10mb range, the effect of the remaining "air" on objects is virtually non existent...I even did the feather vs a quarter test in a 24" tall chamber with viewing glass...they fell at virtually the same speed...In order to get that remaining air to move anything in that chamber (we used it specifically to blow extremely fine dust off very high-tech ceramic circuit boards) we had to use extremely high pressure air, the reason was there just wasnt enough force at 10mb to move much of anything.

When I see particle sizes in the 1/4 to 1+mm range moving with the sand dunes, and the sand dunes themselves, I cant help but wonder exactly what force at 6.5mb and 7 to 70 ft/sec move those particles that are thousands of time larger than the 2 micron particles that AMES moved with 230 ft/sec / 156 mph winds.

I take what I see and try to make better sense of it, without being stubborn and assuming someone else "got it right".

The math wont lie.