Slashdot Mirror
NASA Reveals Dust Devil Data from Mars
saskboy writes "NASA reports that Martian dust devils could be much more destructive than previously considered. You may remember this past April when it was revealed that whirlwinds actually helped the current rovers by cleaning accumulated dust from their solar cells which increased their energy collection efficiency.
But after studying the mini-storms more, they realize that the dust and sand particles could cause static electricity discharges, also known as lightning. The high speed grains of sand blowing around at about 30 meters/second (70 miles per hour) are nothing to blink at either, since they can damage astronauts or equipment on the Martian surface. The height of a Martian dust devil can reach 10km (6 miles), which means it's more like the size of a terran tornado."
The martian atmosphere is much thinner.. so it isnt gonna be as powerful as "terrestrial hurricanes" for sure..
It was in eastern Washington state - many of them were spinning over hot, dry recently tilled farmland.
My friend and I were on a road trip, and I asked him to pull over.
I ran into this thing, and it was really weird - the air around it was still, but the dust devil itself was really windy inside!
It took only a second or two to walk in and out of it, but it was an interesting experience.
The height of a Martian dust devil can reach 10km (6 miles), which means it's more like the size of a terran tornado
But no where near the destructive force of a tornado, which may be why they're calling them dust devils...
It's less than 1/3 the windspeed and since the atmosphere is less dense the total energy will not be anywhere close...
Goofy, Geeky Gifts and More!
They bring up an interesting problem in the article about the difficulty of cleaning surfaces after a storm- the triboelectric charges wouldn't necessarily have anywhere to bleed off to. Since Earth's ground is relatively wet, simply sticking a copper rod into the ground provides a good path for stray charges to go. Unfortunately, in a dry soil like that of Mars, grounding rods may not provide the level of protection they might on Earth. On the other hand, the reduced atmospheric pressure and lowered breakdown potential might actually help simpler methods like the charge dissipators (so called "static wicks") on plane wings. Basically, as long as there is a sharp point to help field emission and concentrate the E field in a small volume of space, the excess charge is dissipated into the atmosphere.
The OP notes the "he high speed grains of sand blowing around at about 30 meters/second".
Just to be clear, we're not talking about "sand" in the sense that your average beachgoer thinks of it. The typical size of the dust grains on Mars is a few tens of microns (say 10-30m or so), which is quite a bit smaller than sand, which ranges from a few hundredths of a millimeter to a couple millimeters in size (roughly, using geological definitions).
No gods, no demons, and no masters. Secular Humanism!
Both tornados and dust devils happen when the air close to the ground is warmer than the air up a bit higher. In tornados, there is a lot more power generated over a larger area (and has the potential to do more damage) than a dust devil would.
Because of the thin martian air, the dust devils have little destructive power so they aren't called tornados.
A fine is a tax you pay for doing wrong and a tax is a fine you pay for doing all right.
A couple of months ago NASA posted some even better videos of the Martian dust devils, available here:
http://photojournal.jpl.nasa.gov/catalog/PIA07139
http://photojournal.jpl.nasa.gov/catalog/PIA07140
http://photojournal.jpl.nasa.gov/catalog/PIA07138
There's also a rather neat video of Opportunity escaping from the sand trap.