So what are these things? If you follow Mars news, you might guess they’re Martian “blueberries”, those BB-sized concretions that form when water dissolves minerals inside rocks which precipitate as hard little pellets. Concretions, excellent indicators of formerly wet environments, are found both on Earth and Mars.
Nope, these are different.
“This is one of the most extraordinary pictures from the whole mission,” said Opportunity’s principal investigator, Steve Squyres of Cornell University. “Kirkwood is chock full of a dense accumulation of these small spherical objects. Of course, we immediately thought of the blueberries, but this is something different. We never have seen such a dense accumulation of spherules in a rock outcrop on Mars.”
The spheres are just 3 mm in diameter or just over a tenth of inch in diameter. If you look closely, you’ll see some of them have a concentric structure where the wind has eroded away the exteriors. According to Squyres, they’re crunchy on the outside and softer on the inside. Kind of like chicken nuggets. Well maybe not exactly like nuggets, but you get the idea.
While scientists are working out various hypotheses as to their origin, allow me to suggest one. Fair warning, this is only a hunch. Up north of Duluth on the Gunflint Trail near Grand Marais, Minn., geologist Mark Jirsa discovered outcroppings of rock composed of layers of small spheres with concentric structures several years ago. After analysis, Jirsa determined they were created in the fiery maelstrom following the impact of a small asteroid that created the Sudbury Impact feature in nearby Canada. In the rising cloud of ejected material ash and vapor coalesced to form small spherical rocks with concentric layering, much the same way hailstones form. These fell back to Earth in Minnesota (and other places) and over time became cemented into a layer of rock. Other types of lapilli are released during volcanic eruptions.
It’s possible that one or both of these two scenarios happened on Mars. I can’t wait to see what further studies of the new spheres will show. If you’re interested in Jirsa’s research, please check out this short, readable paper on the topic.