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.
That, anyway, is the leading explanation. The spidery traces that you see in Michael's two prints might be clumps of dark, basaltic sand thrown from the geysers. Or — say a group of Hungarian scientists — they might be colonies of photosynthetic Martian microorganisms, warmed from the sun, now sunbathing in plain view. We still don't know for sure.We've been watching those spider patches come and go for the last decade or so, and for a little while longer, we will have to guess why they're there, or what they're telling us.
We'll have to keep looking.
A 2006 letter in Nature described this idea of geysers near the Martian south pole. Some American scientists then proposed a "Mars Geyser Hopper," an instrument built to investigate geysers that could "hop" from site to site. (Avoiding, one presumes, sudden gushers from below). Michael Benson's new collection of prints, taken from the digital printouts transmitted by exploration space telescopes, are works of science and imagination. The images are black and white in origin; the color is added. Michael calls his technique "true" color, meaning, he's choosing a spectrum that represents what a human eye would see if a human eye (and brain) were on the scene. His newest is called "Planetfall: New Solar System Visions."