Dust Devils
Dust Devil on Mars - photographed by the Mars rover Spirit.
They are a popular phenomen on Mars.
They apear frequently on Mars (and Earth) when it's HOT and then they move around totaly randomly in packs.
On Earth they come in different sizes with a couple o metres diameter and a hight of 30 m. On Mars they are HUGE! (due to the low gravity, rapid temperatures schift, lots of dust and low humididty). The biggest Martian Dust Devils can be as tall as Mount Everest! (check this picture:
http://www.msss.com/mars_images/moc/8_10_99_releases/moc2_171/moc2_171d_msss.jpg)
They induce a high level of electrostatic charge so many electronic equipement near them (like radio) doesn't work.
They are not tornados. They don't need a cloud that would make one. All they need to appear is a worm ground.
Also - the difference between the dust devil and the tornado is that a tornado starts from the sky and then touhes the ground. Dust devil starts from the ground and rises up.
You may remember a very scary Dust Devil from the film "Mission to Mars" where it kills the crew
And that scene on youtube:
http://www.youtube.com/watch?v=O8DJDMT6JoAFor more information about them, please check the links below.
http://www.islandnet.com/~see/weather/almanac/arc2008/alm08jul.htm http://www.msss.com/mars_images/moc/8_10_99_releases/moc2_171/I think it's only natural to add them into MCO. 
FAQ:When does they appear?On Mars -
They are most frequent on Martian spring or summer days, first appearing about 10 am (local time) as the ground heats and ending about 3 pm when the ground begins to cool. (Mars' solar day is 24 hours 39 minutes long.)
How long do they live?On Earth -
The majority of dust devils are small, usually less than 1 metre in diameter, and rather short-lived, lasting a couple minutes or less. The longer-lived and larger devils, however, garner the most attention. The largest can expand to 300 metres wide and hundreds of metres high, but most often they are only a few metres in diameter and less than thirty metres tall. Their life spans are typically fifteen minutes, though a well-established devil can persist for an hour or more.
How fast do they travel?On Mars -
It crossed the Martian terrain at a speed of about 4.8 metres per second (16 feet per second) and covered a distance of about 1.6 km (1 mile).
What happens if they encounter an obstacle?-An obstacle can be a rock, a building, terrain change, vehicle, man, etc.... If they come across the Dust Devil they drop it off the balance and the Dust Devil dissapears.
What happens to man and machines that crosses the Dust Devil way?-Machinery can be dammaged due to the electrostatic power and the dust it carries.
On Earth - they kill peeple very rarelly, only in very specific ways (like droping some objects on a head)
On Mars - they are a very big probblem. They can dammage the EVA easily and therefore - couse a man do die. Let's also not forget that Dust Devils are very common on Mars.
Do they leave any trace behind?-Yes. They leave behind a dark streak of dirt that they digged out.
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Also - please take a look at the pictures below.
