At the beginning of his mission, the Opportunity Rover discovered round, iron-rich concretions nicknamed "blueberries." This was one of several evidences indicating that Mars was wet. This (false-color) photo covers an area of only 3 cm.
Photo credit: NASA / JPL-Caltech / Cornell / USGS
It was only months after NASA's opportunity rover landed on Mars in 2004 that he discovered a geological curiosity: tiny, iron-rich bullets flying over the rock surface were scattered near the landing site of the robot. Snack-loving scientists who worked with the mission called these objects "blueberries," but the features were easier to name than to understand. Your recipe remains a mystery.
To find out the origin of these blueberries, you have always looked for similar looking globe formations on Earth. New research is based on these terrestrial analogues to give a new idea of the chemistry that might have set these Mars blueberries. This research in turn helps to show what old Mars might have looked like.
The bilberries lure with more than just their quaint name; They were also some of the first evidence we had that Mars was incredibly wet once. "Whatever the exact chemistry of these globules should be, the fact that they are there tells us [that] that over time, much liquid water moved through these rocks," said Briony Horgan, a planetary scientist at the Purdue University in Indiana told Space.com. [1
And if scientists can figure out exactly how the blueberries formed, it could help us to understand what Mars looked like when the facial features were formed – and what kind of life theoretically could have thrived in those circumstances, said Horgan.
So, the team behind the new research traveled to two different destinations in search of rock formations reminiscent of Marian blueberries: Utah and Mongolia. These formations are not identical to those on Mars, which are about one tenth the size of earthly equivalents. The formations of our planet are also less ordered than the Mars versions. "They're all blurry together, they're different sizes," Horgan said about the terrestrial features.
But it's much easier to get to Utah and Mongolia than to Mars. Therefore, scientists use these properties despite the incomplete comparison. The researchers found that the formations were built around cores of a mineral called calcite, with iron-rich material only in the outer shell. "This moment [of discovery] was very exciting," wrote geo-chemist Hidekazu Yoshida of Nagoya University and Hitoshi Hasegawa of Kochi University in Japan in an e-mail to Space.com.
Based on these observations in the field and chemical modeling, the scientists suggested that floods of iron-rich, slightly acidic water flooded the original calcite structures. Unlike the terrestrial versions, Marian blueberries seem to be made all the way from hematite and do not contain any calcite heart anymore. However, the researchers could point to a long period of washing through the entire calcite.
The nagging details of chemical reactions that may or may not have occurred on early Mars have greater implications. First, these details are relevant to scientists' natural interest in all the water that flows through rocks to blueberries. "The chemistry of water tells us about the habitability of the environment," Horgan said.
The second possible implication would refer to another long-standing debate about Mars – what happened to its once-thick atmosphere. The authors of the new study argued that this atmosphere could have penetrated into the carbonate ions trapped in calcite precursors for the blueberries.
But that would not solve the atmospheric mystery, Steve Ruff, a planetary geologist at Arizona State University, who works on the opportunity mission, Space.com said. "My sense of what we know about the area of hematite we can map out of orbit is that it's not a huge area," he said. There just are not enough blueberries to pack the atmosphere. [Latest Mars Rover Photos from Opportunity & Spirit]
He said he also worried that the Earth's formations were not similar to those on Mars, so scientists could learn about the blueberries. But Ruff has not rejected the new newspaper. "I am fascinated by this idea," he said. "Forming these little concretions on Earth and certainly on Mars has always been a mystery, and there are several ideas on how to shape those things."
The Mars blueberries are small enough to really solve them It's a mystery that scientists will need more complex tools than they currently have on the Red Planet. NASA's next rover, the Mars 2020 Rover, will carry instruments with such a high resolution that they can solve those questions. But the rover is to visit a place called Jezero Crater, far away from the level where Opportunity discovered the blueberries.
"With NASA returning to places on Mars is not something people do not want, they want to go to new places," said Ruff. Nevertheless, he said that he does not give up hope that the new rover could solve the blueberry secret. "Maybe we'll see something like this with the 2020 Rover and see something like that."
Whatever the nuances of blueberry chemistry, the new paper reminds of the enormous time scales – and the potential complexity of those times – Involved in Martian geology, Horgan said. "In the minerals we see, time can play a really important role," Horgan said. "We should be careful, there may have been several things that happened to these rocks."
The research is described in an article published today (December 5) in the journal Science Advances.