A few NASA rovers have been working their way through the Red Planet, each working to expand scientists' knowledge of Mars and its history. As part of this, large quantities of images are taken and shuttled back to Earth, where researchers analyze them. Recently, the rover Opportunity sent back two images of the same area that had one surprising difference: the sudden appearance of a rock that hadn't been there shortly before.
The small rock, described as being about the size of a jelly doughnut by NASA's Steve Squyres in an interview with Discovery, was announced at a NASA Jet Propulsion Laboratory event yesterday night. The photo with the mysterious rock appeared earlier this week, with the small chunk of material being positioned a few feet in front of the Opportunity rover.
The images, which were taken with Opportunity's Pancam, show bare bedrock in sol 3528 (featured on the left in the image above), while sol 3540 shows the same area, only with the addition of the relatively small rock. Said Squyres: "It was a total surprise, we were like 'wait a second, that wasn't there before, it can't be right. Oh my god! It wasn't there before!' We were absolutely startled."
No one is quite sure how the rock made its sudden appearance, but there are a couple theories at the moment. The first, and currently most probable, is that the rover somehow "flipped" or otherwise moved the rock there while it was moving, or that the rock landed there from a meteorite impact while Opportunity was "looking" away. The first is considered most likely because one of Opportunity's front actuators, which is used to steer, no longer works, and so when the rover turns, it kind of scraps across the ground and could fling a rock a short distance as a result.
Regardless of how it got there, scientists have been given a nice opportunity for additional study because of it. The rock landed upside down, and so a portion that has not been exposed to the surface is now visible for analysis. This doesn't mean NASA is closing the book on the mystery, however -- an investigation is still underway to try and determine the cause.