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© Universe TodayScreenshot from Steve Squyres presentation celebrating 10 years of the Mars Exploration Rovers. A rock suddenly appeared where there was none 12 sols earlier.
During last night's celebration at the Jet Propulsion Laboratory of ten years of the Mars Exploration Rovers, mission principal investigator Steve Squyres shared several stories about the exploration and discoveries made by the rovers Spirit and Opportunity since they landed on Mars in 2004.

An intriguing recent mystery is a strange rock that suddenly appeared in photos from the Opportunity rover in a spot where photos taken just 12 sols earlier there was no rock.

"One of the things I like to say is that Mars keeps throwing new things at us," Squyres deadpanned.

Squyres described the rock as "white around the outside, in the middle there's low spot that is dark red. It looks like a jelly donut," he said. "And it appeared. It just plain appeared and we haven't driven over that spot."
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© NASA/JPL, color by Stuart AtkinsonA colorized version of the rock called Pinnacle Island.
They've named it "Pinnacle Island," and the team is contemplating a few ideas of why the rock mysteriously showed up.

"One theory is that we somehow flicked it with a wheel," Squyres said. "We had driven a meter or two away from here and somehow maybe one of the wheels managed spit it out of the ground. That's the more likely theory."

The other?

"The other theory is that there might be a smoking hole in the ground nearby and this may be crater ejecta. But that one is less likely," Squyres said.

Another idea suggested by others is that it may have tumbled down from a nearby rock outcrop.
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© NASA/JPLImage from Sol 3528 of the area showing no rock. Click to see original on the rover’s raw image website.
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© NASA/JPLImage of same area on Sol 3540 where the ‘jelly donut’ rock appears. Click to see original.
But as intriguing as the sudden appearance of the rock is what the team is finding out about it.

"We are as we speak situated with the rover, with its instruments, making measurements on this rock. We've taken pictures of both the donut part and the jelly part," Squyres said. "The jelly part is like nothing we've seen before on Mars. It's very high in sulfur and magnesium and it has twice as much manganese as anything we've seen before. I don't know what any of this means. We're completely confused, everybody on the team is arguing and fighting. We're having a wonderful time!"

But that's the beauty of this mission, Squyres said.

"I used to have this comforting notion that at some point, we could sit back and say 'we did it, we're finished, we've learned everything we could about this location.' But Mars is not like that. It keeps throwing new things at us."

"And what I've come to realize," Squyres concluded, " - and it was true when we lost Spirit and it will be true when we lose Opportunity - there will always be something tantalizing just beyond our reach that we just won't get to. That's just the nature of exploration, and I feel so very fortunate to have been part of this mission."

You can watch the entire replay of the celebration below, and read a great look back at the past 10 years from Stuart Atkinson's Road to Endeavour blog.