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The Case of the Opportunity Rover and the Mysteriously Appearing Martian Rock

Probably not evidence of meddlesome Martian youth, but still.

by Amy Shira Teitel
Jan 19 2014, 9:43pm
The appearance of Pinnacle Island/NASA via Discovery

After nearly a decade on Mars, NASA’s Opportunity rover is still finding things that surprise us. The latest is a mysterious rock that appeared just feet from the rover; a raw image from Opportunity’s panoramic camera (pancam) from Sol 3528 shows no rock, then the same view on Sol 3540 (Jan. 8, or the 3,540th Martian solar day) shows what the team are saying is a doughnut-sized rock. They’ve since named it “Pinnacle Island.” Martian magic isn’t the likely culprit in the case of the appearing rock, but it is nevertheless interesting (albeit more for the scientists than the layman) and another in a long list of surprise discoveries by the veteran rover.

There are a couple of ways to explain the rock’s sudden appearance, reports Discovery News. The rover could have knocked it or flipped it over while maneuvering around, or it might've landed there by chance as ejecta from a meteorite impact. For the moment, mission scientists are going with the former idea since none of the mission scientists has yet found a fresh, smoking crater near the rover.

That Opportunity knocked it loose is, on the other hand, a likely explanation. The rover has six wheels, each of which has an actuator that makes it turn. But one of Opportunity’s front wheel actuators has experienced problems lately and isn’t turning like it should. When the rover turns, that one wheel sort of skids along the surface. In an area with broken bits of rock, like the bedrock the rover was sitting on when it found the mystery rock, the skidding wheel could catch and toss a rock.

The mission’s lead scientist Steve Squyers suspects this is just what happened. But the ordinary event has come with an extraordinary stroke of luck. The rock flipped over when it moved, meaning it’s now showing the rover a side of itself that hasn’t seen the Martian atmosphere is perhaps billions of years. That’s something different, and exactly what the MER team likes to see.

This is far from the first time Opportunity, which landed on Mars on Jan. 25, 2004, has found something exciting and unexpected. The rover landed, incredibly, in a 66-foot wide shallow crater called Eagle Crater. As Squyers described the landing point, “we scored a 300 million mile interplanetary hole in one.” And before it drove away from its landing spot the rover found something incredible: tiny spherules of hematite the team called “blueberries.” It was an exciting find because on Earth hematite is only formed in the presence of water. Right away Opportunity found compelling evidence for a past wet Mars.

Opportunity was built to last 90 days on Mars, but as we know it kept going and the mission has been extended multiple times. The rover has to date driven a little more than 24 miles. And throughout its extended mission the interesting discoveries have kept on coming. In 2009, it found a meteorite, the first ever discovered on another planet. In the summer of 2009 (Earth time), the rover approached a large cobbled rock about two feet across called “Block Island.” After targeting the rock with its instruments, Opportunity confirmed that it was an iron-nickel meteorite. Weeks later it found another, smaller meteorite called “Shelter Island.”  In 2011, Opportunity found more evidence of past water on Mars in the form of a mineral vein of gypsum that could only have been left by water. On this discovery, Squyers said it tells “a slam-dunk story that water flowed through underground fractures in the rock. This stuff is a fairly pure chemical deposit… it's the kind of thing that makes geologists jump out of their chairs.”

While finding gypsum, meteorites, hematite spherules, and now a previously unexposed face of a rock are all exciting discoveries, they mean a lot more to the mission scientists who understand them than to the average armchair Mars enthusiast. Especially since the real work only begins after the initial excitement of the find has ebbed. The science team behind Opportunity will make Pinnacle Island the rover’s main target for the next few days. In a few weeks, we should get more information on the mystery rock. What the team finds might not be groundbreaking to everyone, but it’s certain to add to the absolutely incredible wealth of information and data Opportunity has already extracted from our planetary neighbor.