For more than a decade, scientists have seen them: black, spidery forms appearing on the surface of Mars with a strange regularity. But what are they? How do they get there? Was David Bowie right about the Spiders from Mars?
Well, sadly, they're not alien spiders from the Red Planet, but they are a strange phenomenon that still doesn't have a conclusive explanation. Since 1998, images like this one have been perplexing scientists.
The above photo (which, trust us, you'll really want to click and take a closer look at) was taken in 2010 by NASA's Mars Reconnaissance Orbiter and later turned into a color print by photographer Michael Benson. It's a view from 200 miles above the surface of Mars, and it shows several dozen spidery black flecks lining the Martian sand dunes. We've been seeing them every Martian spring for the last 14 years, and we still don't know for sure what they are. But, of course, there are some theories.
First, it's important to understand just how these black spots seem to work. They react to heat. When spring arrives, they appear. As it gets hotter, they seem to spread. Then, when winter comes, they're gone. They also only appear on the dunes, never on the plains.
The most prominent explanation for this is that the black patches are the result of explosions of frozen carbon dioxide heated by the sun, exploding up from under the surface through cracks.
"If you were there," said Phil Christensen of Arizona State University, "you'd be standing on a slab of carbon dioxide ice. All around you, roaring jets of carbon dioxide gas are throwing sand and dust a couple hundred feet into the air."
These powerful geysers might just be throwing up dark sand from beneath the surface. Or, according to a theory proposed by Hungarian scientists, they could be shooting up colonies of dark microorganisms which then retreat back into the ground when it gets cold. We still don't know, but either way this phenomenon definitely dispels the idea that Mars is just a boring lump of red dirt.