Left: a photo taken 3528 days after the Opportunity rover arrival to Mars. Right: the exact same spot 12 Mars days later. Notice the difference? NASA JPL scientists did too: "It's about the size of a jelly doughnut. It was a total surprise, we were like 'wait a second, that wasn't there before, it can't be right. Oh my god! It wasn't there before!' We were absolutely startled."


Those were the words of NASA Mars Exploration Rover lead scientist Steve Squyres at a special event celebrating a decade of Mars rover exploration, which took place yesterday night at the California Institute of Technology in Pasadena, California.

Scientists don't exactly know how the hell the rock appeared there. Did a Martian throw it? Did it magically materialize? He told Discovery News about their theories:


The first is that the rock "just landed there," ejected from a meteorite impact close to the area. The second theory is that the rover pushed it with one of the wheels that is now jammed.

So my best guess for this rock … is that it's something that was nearby. I must stress that I'm guessing now, but I think it happened when the rover did a turn in place a meter or two from where this rock now lies. So if you do a turn in place on bedrock, as you turn that [broken] wheel across the rock, it's gonna kinda 'chatter' [flipping the rock over]. It obligingly turned upside down, so we're seeing a side that hasn't seen the Martian atmosphere in billions of years and there it is for us to investigate. It's just a stroke of luck.

And of course, there's always the third theory:

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