classic-movie-spiderMars is largely perceived as a lifeless wasteland of rock, dirt and endless dunes. Not exactly a place you’d want to visit, or even explore. But a new theory suggests there’s much more activity taking place on the Red Planet than previously thought.

First discovered back in 1998, scientists have been stumped by the appearance, and subsequent disappearance, of jet black material dotting the planet’s surface; like “sunbathing spiders sitting in rows,” NPR described. You can see them in both the up-close and satellite image below. What the?

Scientists have no clue what they are, and what’s really strange about the find is that they appear seemingly out of nowhere, sometimes overnight. For the most part — at least 70 percent of the time — they show up in the same place, too. Their appearances have been narrowed down to “every Martian spring,” NPR said, and disappear once temperatures begin to drop in the winter.

“As the sun gets hotter, they get more spidery,” NPR explained. “The spidery thingies, you’ll notice, stay on the rise, not on the flat sandy plains.”

The leading theory from the U.S. Geological Survey surmises that the culprit is Martian geysers. As the surface warms, a layer of underground CO2 unfreezes and expands. This creates an explosion of rock and ice a couple hundred feet high. The spidery mirage may just be left over remnants, a dark mixture of basaltic sand.

A more wild explanation, according to a group of Hungarian scientists, suggest the little black traces are actually “colonies of photosynthetic Martian microorganisms, warmed from the sun, now sunbathing in plain view,” NPR wrote. Wouldn’t that be something?

[via NPR]