This mysterious rock just appeared in front of our rover on Mars

A mysterious rock suddenly appeared in front of the Opportunity rover's cameras on Mars, puzzling scientists who describe the rock as both "a total surprise" and "about the size of a jelly donut."

The news of the rock, which NASA scientists have dubbed "Pinnacle Island", came during a talk by Mars Exploration Rover head scientist Steve Squyres during the 10th anniversary celebration for the Mars rovers. Though scientists aren't sure exactly where the rock came from, or really much about it at all, they have a couple theories. Discovery reports:

Only two options have so far been identified as the rock's source: 1) The rover either "flipped" the object as it maneuvered or, 2) it landed there, right in front of the rover, after a nearby meteorite impact event. The impact ejecta theory, however, is the least likely of the two. "So my best guess for this rock … is that it's something that was nearby," said Squyres. "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." Opportunity's front right steering actuator has stopped working, so Squyres identified that as the possible culprit behind the whole mystery.

Whether the rock landed there, was knocked there, or was placed there by a friendly alien as a gift for its newest robot friend (note: it was not that last one), it could offer a scientific opportunity beyond the mystery of its origin, says Squyres:

"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."

Image: NASA-JPL, via Discovery.