Image from the panoramic camera (Pancam) on NASA’s Mars Exploration Rover Opportunity showing the location of a rock called "Pinnacle Island" before it appeared in front of the rover in early January 2014/NASA JPL
Remember the weird rock that just appeared one day on Mars in a picture taken by NASA’s Opportunity Rover? The rock that looked like a jelly doughnut? The one over which a man sued NASA claiming the agency was ignoring obvious signs of Martian life? Well, the mystery has been solved. The rock, it turns out, is really just a rock.
The rock in question is small, measuring about 1.5 inches across, and caught the world’s attention on Jan. 8 when it appeared in one of Opportunity’s panoramic camera images where it hadn’t been the day before.
The rock first appeared in a raw image taken by Opportunity’s panoramic camera (or pancam) on Sol 3540 (the 3,540th day of the rover’s mission, which corresponds to Jan. 8, 2014 on Earth). The image showed a 1.5 inch rock where there hadn’t been one 12 Sols previously, and it looked a little lille a jelly doughnut. Colour images showed it was white around the edges with a slightly reddish tinge in the centre. The science team behind Opportunity named the rock “Pinnacle Island,” and while its sudden appearance was a surprise the science team had some pretty mundane explanations for its genesis.
The likeliest cause was that the rock was kicked up by the rover. One of the rover’s six wheels has a problematic actuator meaning it doesn’t turn when the rest of the wheels do. Instead, it skitters across the surface as the rover moves around. This skidding over broke rocks could easily have kicked up the jelly doughnut.
It seems like this is indeed the explanation behind the rock. More recent images of the same area show what looks like the piece of rock Opportunity rolled over to dislodge Pinnacle Island, slightly uphill from where the jelly doughnut came to rest. “Once we moved Opportunity a short distance, after inspecting Pinnacle Island, we could see directly uphill an overturned rock that has the same unusual appearance," said Ray Arvidson, Opportunity's deputy principal investigator. And the picture show the sequence of events. "We drove over it. We can see the track. That's where Pinnacle Island came from.”
But Pinnacle Island’s origin was only ever part of the rock’s interest. When the rock moved it flipped over, showing a side of itself that hasn’t seen the Martian atmosphere is billions of years meaning its untainted by that atmosphere.
Scientists have been studying the newly exposed rock face and found high levels of these elements manganese and sulfur, two elements that suggest were concentrated in the rock by water. "This may have happened just beneath the surface relatively recently," said Arvidson, "or it may have happened deeper below ground longer ago and then, by serendipity, erosion stripped away material above it and made it accessible to our wheels.”
The mystery of the appearing rock solved and the more important scientific data gathered, Opportunity is getting ready to leave Pinnacle Island behind. The team is planning to drive the rover uphill where it will investigate the exposed rock layers on the slope. Opportunity is slowly making its way to a boulder-studded ridge called the McClure-Beverlin Escarpment. Jack Beverlin and Bill McClure were the first recipients of NASA’s Medal of Exceptional Bravery for saving Mariner 6 by preventing its Atlas launch vehicle from collapsing and exploding on the launch pad in 1969.
This next step for Opportunity exploring the north-facing slope below the escarpment will be tilting its solar panels towards the Sun, a welcome boost since Opportunity has been working through Mars’ winter recently. ”We are now past the minimum solar-energy point of this Martian winter," said John Callas, Opportunity Project Manager. "We now can expect to have more energy available each week. What's more, recent winds removed some dust from the rover's solar array. So we have higher performance from the array than the previous two winters.”