The Sciences

The Devil is in the details

Bad AstronomyBy Phil PlaitSep 30, 2005 1:31 AM


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The other day I was in the car with Mrs. Bad Astronomer, and while we were stopped at a light she suddenly pointed out the window and shouted, "Dust devil!" I took a look, and sure enough, there was a little swirl of wind circling around in front of the car. It was about a foot across, and had picked up some leaves and detritus, whirling around like a miniature and delicate tornado. Dust devils are in fact similar to tornados, but are not nearly so violent. I've seen lots of them, from small ones that can barely pick up leaves, to a big one once when I was in college. That one had formed -- I think -- due to the unusual shape of a building. Wind would come around the building, create a vortex, and was fed by warm air in the surrounding field. It was easily two or three meters across, and maybe 15 meters high. I watched it for quite a while, 10 or 15 minutes at least, as it would wander away from the building, wander back, pick up leaves, fling them around. It was fascinating! It's been known for a while that dust devils are not restricted to Earth. Mars is blighted with them.

Orbiting spacecraft show the view from a height. In the image above, we are looking straight down on a few of the devils. You can see their shadows above them! There are countless images like this one. As the funnel sucks up the sand beneath them, they leave the darker rock exposed, and so many images show winding, spiraling dark trails across the martian surface. Then we landed rovers on the surface! Suddenly, dust devils got even more interesting, because we could see them from the side. Here's an image from one of the rovers:

Not only that, but multiple images could be taken, and made into animations. You can watch them move! Atmospheric Scientist Mark Lemmon at Texas A&M University shares my fascination with these beasties, but he has access to the data, and the tools to make the data even cooler. On his website he has collected dozens of these events, and has created very cool animations from them. By watching those movies, you are seeing weather on another planet. Do I even have to say it? Science is so cool!

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