https://www.space.com/42645-mars-blueberries-formation-mystery-earth-analogs.html

It was just a few months after NASA’s Opportunity rover touched down on Mars in 2004 that it spotted a geological curiosity: tiny, iron-rich spheres scattered across the rock surface near the robot’s landing site. Snack-loving scientists working with the mission dubbed these objects “blueberries,” but the features were easier to name than to understand. Their recipe remains something of a puzzle.

Trying to sort out the origins of these blueberries has always involved studying similar-looking spherical formations here on Earth. New research takes its inspiration from these terrestrial analogs to offer a new idea of the chemistry that may have gone into whipping up these Martian blueberries. In turn, this research helps reveal what ancient Mars may have looked like.

The blueberries are tantalizing for more than just their whimsical name; they also constituted some of the earliest evidence we had that Mars was once incredibly wet. “No matter what the exact chemistry of these spherules was to start, the fact that they’re there tells us [that] a lot of liquid water moved through these rocks over time,” Briony Horgan, a planetary scientist at Purdue University in Indiana, told Space.com. [10 Amazing Mars Discoveries by Rovers Spirit & Opportunity]

And if scientists can parse out precisely how the blueberries formed, that may help us understand what Mars was like back when the features formed — and what sort of life could have theoretically thrived in those circumstances, Horgan said.

The nagging details of chemical reactions that may or may not have taken place on early Mars have larger implications. First, these details are relevant to scientists’ natural interest in all that water that flowed through rocks to form the blueberries. “The chemistry of water tells us about the habitability of the environment,” Horgan said.

The second potential implication would relate to another long-standing debate about Mars — what happened to its once-thick atmosphere. The authors in the new study argued that this atmosphere could have gone into the carbonate ions locked in calcite precursors to the blueberries.

But that wouldn’t solve the atmospheric mystery, Steve Ruff, a planetary geologist at Arizona State University who works on the Opportunity mission, told Space.com. “My sense of what we know about the area of the hematite that we can map from orbit is it’s not a huge area,” covering less than 1 percent of Mars’ surface, he said. There just aren’t enough blueberries to pack away very much atmosphere. [Latest Mars Rover Photos from Opportunity & Spirit]

He said he also worries that Earth’s formations aren’t similar enough to those on Mars for scientists to learn about the blueberries. But Ruff didn’t dismiss the new paper. “I’m intrigued by this idea,” he said. “The formation of these little concretions on Earth and certainly on Mars has always been a bit of a mystery, and there’s multiple ideas about how you form these things.”