"You are 200 miles directly above the Martian surface — looking down. This image was
taken by the Mars Reconnaissance Orbiter on Jan. 27, 2010. (The color was added later.) What do we see? Well, sand, mostly. As you scroll down, there's a ridge crossing through the image, then a plain, then dunes, but keep looking. You will notice, when you get to the dunes, there are little black flecks dotting the ridges, mostly on the sunny side, like sunbathing spiders sitting in rows. Can you see them?"
taken by the Mars Reconnaissance Orbiter on Jan. 27, 2010. (The color was added later.) What do we see? Well, sand, mostly. As you scroll down, there's a ridge crossing through the image, then a plain, then dunes, but keep looking. You will notice, when you get to the dunes, there are little black flecks dotting the ridges, mostly on the sunny side, like sunbathing spiders sitting in rows. Can you see them?""What are those things? They were first seen in 1998; they don't look like anything we have here on Earth. To this day, no one is sure what they are, but we now know this: They come, then they go. Every Martian spring, they appear out of nowhere, showing up — 70 percent of the time — where they were the year before. They pop up suddenly, sometimes overnight. When winter comes, they vanish."
"As the sun gets hotter, they get more spidery. Here's a closer image — like the one above, this gorgeous print was created by the photographer Michael Benson, just published in his new book, Planetfall. It shows two mounds of sand. The spidery thingies, you'll notice, stay on the rises, not on the flat sandy plains."