Sand Dunes On Mars In Motion

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."

If you walk without rhythm

[Anonymous Coward]

you won't attract the worm

Re:Controlled for all factors?

[Baloroth]

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?

[WillHirsch]

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.