My colleague noticed something strange in the latest batch of photos from NASA’s Perseverance Mars rover: A roundish rock appears to be carefully balanced atop a jagged outcrop. How did that get there?
The photo was taken in Mars’ Jezero Crater by Perseverance’s right Mastcam-Z on Sol 466, which corresponds to June 12 here on Earth.
I emailed NASA to ask what the rock could be and whether there’s anything truly strange here. James Rice, a geologist on the Mastcam-Z team from the School of Earth and Space Exploration at Arizona State University, wrote back to me:
Balancing rocks (sometimes called Precariously Balanced Rocks PBRs) of various sizes, ranging from small rock sizes (inches) to formations hundreds of feet high, are naturally occurring and not really that unusual. Often a balancing rock is in fact connected to the larger underlying rock by a stem or pedestal. The Martian balancing rock shown is found at the Rockytop outcrop near the base of the delta and was most likely formed after extensive aeolian (wind) and/or chemical erosion carved it out from the local bedrock.
These types of features are more than just geologic curiosities; in fact they have been called “reverse seismometers” because the existence of PBRs makes it possible to measure earthquakes/marsquakes that didn’t happen. If these rocks are still balanced, then the ground hasn’t moved enough to knock them over. So we can use these features to learn about a region’s seismic history.
Ah yes, a classic PBR. Glad that’s cleared up!
Around the same time as this image, the Perseverance rover got a photo of a shiny piece of material tucked into some rocks, and NASA believes it could be a piece of the rover’s thermal blanket from its landing in 2021. NASA tweeted that the rover landed 2 kilometers (1.25 miles) away from where the blanket remnant was found, but notes that it could’ve been moved by the wind or landed there by itself.
We get weird images from Mars all the time, and we’ve seen rocks that look like squirrels, spoons, doorways, and more. Our eyes play tricks on us, and that’s especially true when viewing an alien landscape full of both familiar and unfamiliar sights. We’re seeing two-dimensional representations of a three-dimensional world, so these optical illusions are bound to happen.