The Curiosity rover has been cruising around on Mars since late 2012, so you’d think that scientists would have a pretty good handle on the kind of data it’s been sending back by now. However, some of the latest readings the rover has taken are totally contradicting many of the theories scientists have about Mars, and most notably when and how liquid water existed on its surface.

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We — and by “we” I mean scientists that are way more intelligent than you or I — know few concrete things about Mars’ past, but one thing we’re sure of is that liquid water once existed on its surface. There’s been ample evidence to suggest it, and at this point it’s something most scientists assume as fact.

However, in order for liquid water to have existed on the surface of the red planet billions of years ago the conditions would have to have been warm enough, and the models that climate researchers rely on suggest it simply wouldn’t have been. So, a theory arose that perhaps Mars’ atmosphere was so thick with carbon dioxide that the planet was able to remain warm enough to support liquid water, thanks to a greenhouse effect. So with that theory in flux, the Curiosity rover set out to confirm it by sampling bedrock from an ancient lake, assuming it would find ample carbonate materials, thereby supporting the greenhouse warming theory. Well, it didn’t.

“We’ve been particularly struck with the absence of carbonate minerals in sedimentary rock the rover has examined,” NASA’s Thomas Bristow explains. “It would be really hard to get liquid water even if there were a hundred times more carbon dioxide in the atmosphere than what the mineral evidence in the rock tells us.”

In short, Mars researchers just had their best and brightest theory about how liquid water existed on the planet’s surface shot in the foot. Water was there, but how and why are now an even bigger puzzle, and the ever useful Curiosity rover just gave us yet another thing to scratch our collective heads about.

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See the original version of this article on BGR.com

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