Oct 31, 2009

Dust devil

USGS Dune Database Entry

Got this pic from HiRISE.

Take this as a psychological picture test. You know, those kind of test where the psychologist flips a card with a blot of ink on it and ask you tell him/her what cross your mind in the first spontaneous minute.

Usually, if you're answer is butterfly, then you'll be assessed as someone who is innocent or happy or both. If you saw a devil in it, you'll probably just born to be wild or evil or perhaps, both.

Anyway, just take a look at the picture above.

What is your first impression? And yeah, no, this is not a psyche test, so please don't scroll down or look back and front for the psyche interpretation.

For a minute, it looks like a great artwork. Some abstract kind of beautiful art.

Then if you look closer, maybe it is body art, with the skin like texture over the right side and the ?buttcrease or ?cleavage over the upper left.

Honestly it is an artwork. An artwork of nature.
But not on our planet.
In the neighbouring Mars

Those aura-like blue rays are actually caused by dust devils.

see caption

A Martian dust devil spins across Gusev Crater just before noon on March 15, 2005. Photo credit: Mars rover Spirit.

Thanks to Phil Plait & Dr. McEwen, here's the down-to-earth overview explanation of the making of the artwork.

But what this picture so spectacular are the graceful blue-gray swirls arcing across the dunes. These are caused by dust devils, which are a bit like mini-tornadoes. If the ground gets heated, rising air can punch through cooler air above it. This starts up a convection cell, with warm air rising and cool air sinking. If there is a horizontal wind the cell can start spinning, creating a vortex like a dust devil. I’ve seen hundreds of these on Earth, and they are wonderful and mesmerizing to watch.

The important thing to note here is that the sand in the craters of Mars is actually dark grey in color, since it’s made of basalt. The reason it looks red in pictures is because covering the sand is a thin layer of much finer dust, and the dust is what’s red. When a dust devil moves over the Martian surface, it can pick up the very light dust particles, but not the heavier sand grains. So those blue-grey swirls are tracks where the dust devil has vacuumed up the dust, revealing the darker sand underneath. If you look carefully in the tracks, you can see the sand dune ripples are undisturbed. Only the dust is gone.


fibrate said...

Seriously, I thought of Mars when I saw the title - had just watched an "educational" programme on the History Channel! But when I scrutinized the image an Ascaris came to mind, surrounded by overlapping haustrations. Yeah, how nerdy LOL

pilocarpine said...

ascaris... very academic... nerdy.. no..