'Blueberries' on Mars Have a Watery Past. But Scientists Are Still Baffled.

By Meghan Bartels, Space.com Senior Writer | December 5, 2018 02:02pm ET

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.

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