Drum Roll Please...

Like a lot of you, when I first saw this picture, I thought it was water, sand, and a seashell. That's definitely what it looks like. But if that's what it really was, this wouldn't be much of a quiz.

I was impressed with your creativity. A crime scene? Lava? A wet etch-a-sketch? Excellent guesses!

Anna wins the prize for funniest comment. But no, it's not mold either.

Given my preoccupation with APOD, I thought someone might think to check the site. And it's funny to me that even though I saw this picture on APOD, I still thought it was sand and water until I saw the caption:

Flowing Barchan Sand Dunes on Mars

Mars, people. Now, that's just cool.

If you want the scientific explanation for what exactly we're looking at, don't ask me. I'll defer to NASA, as usual:

"When does Mars act like a liquid? Although liquids freeze and evaporate quickly into the thin atmosphere of Mars, persistent winds may make large sand dunes appear to flow and even drip like a liquid. Visible on the above image right are two flat top mesas in southern Mars, where the season is changing from Spring to Summer. A light dome topped hill is also visible on the far left of the image. As winds blow from right to left, flowing sand on and around the hills leaves picturesque streaks. The dark arc-shaped droplets of fine sand are called barchans, and are the interplanetary cousins of similar Earth-based sand forms. Barchans can move intact downwind and can even appear to pass through each other. Over the past few weeks, winds on southern Mars have been kicking up dust and are being watched to see if they escalate into another of Mars' famous planet-scale sand storms."

(Gee, are Mars' planet-scale sand storms famous? News to me.)