February 17, 2014 – All the conspiracy theorists are once more shaking their heads as NASA explained away the rock that appeared in a picture taken by the Martian Rover on January 8th this year (Sol 3540 for Opportunity on Mars). That date happens to be my birthday and I wrote about the mystery rock on two separate occasions because it garnered world wide attention, unlike my birthday.
Well when I read NASA’s initial releases I never saw any mention of the actual size of this mystery rock. Turns out it is just under 4 centimeters (1.5 inches) in diameter. So the analogy to a jelly doughnut which appeared in many media outlets seems inappropriate, more likely no bigger than a Timbit (for those not Canadian, Timbits are the mini doughnuts made by a Canadian food chain from excess dough carved out of the doughnut hole).
So how did a rock fragment suddenly appear in a picture when it wasn’t there several weeks earlier? One of the theories speculated that Opportunity‘s wheels dislodged the rock fragment during transit. So NASA panned the camera on Opportunity to look around and lo and behold discovered that the theory was correct.
The mystery rock came from a parent rock located a few centimeters away. In the picture below you can see the parent at the top of the frame and the mystery rock in the bottom left corner. Those tracks are not footprints but the tread of one of Opportunity‘s wheels.
Opportunity gave both rocks the once over with its alpha particle x-ray spectrometer and microscope. Turns out why the rock looks so different from the surrounding regolith is because it contains very high concentrations of manganese and sulphur. These likely suggest the rock was exposed to water at some point in the past. This could have happened recently or in Mars’ ancient past.
More importantly, Opportunity is still the little rover that can. With Martian summer arriving in its vicinity it is off to study a nearby boulder-studded ridge which shows multiple layers of rock laid down sometime in the last billion years.