Water On Mars
NASA used the Mars Reconnaissance Orbiter to detect areas that could contain clay minerals, evidence of ancient water, that were later investigated by Opportunity. NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

Even after 10 years of exploring Mars, NASA’s Opportunity rover continues to find new evidence that is reshaping our understanding of the red planet. In rock samples from Matijevic Hill, researchers have discovered evidence of a milder environment and ancient water on Mars that was less acidic than was previously believed.

The research, published in the journal Science, was led by Ray Arvidson, Opportunity deputy principal investigator. According to Arvidson, the new rock samples are older than pervious samples collected by Opportunity, giving researchers a look further back into Mars’ past. Arvidson said in a statement, “These rocks are older than any we examined earlier in the mission, and they reveal more favorable conditions for microbial life than any evidence previously examined by investigations with Opportunity.”

Opportunity had help from above as NASA’s Reconnaissance Orbiter picked out potential investigation sites. According to NASA, the orbiter’s onboard mineral-mapping instrument, the Compact Reconnaissance Imaging Spectrometer for Mars, was used to find a location at Matijevic Hill, located at the rim of the Endeavor Crater, that contained smectite, iron-rich clay minerals.

Smectite was discovered on Mars by Curiosity in 2013, indicating the existence of an ancient river or lake bed. The Curiosity findings indicated an environment that was once suitable for life on Mars, and the latest Opportunity findings adds new insights to the history of water on the planet. According to the researchers, the wet environment is older than the Endeavor Crater, which was created approximately 4 billion years ago.

Opportunity previously discovered evidence of ancient water in a location known as Cape York. Researchers discovered evidence of flowing water changing the features of a rock, called “Esperance.” In addition to the evidence of ancient water, researchers discovered soil samples collected by Curiosity contain water, up to 2 percent.

Michael Meyer, lead scientist for NASA's Mars Exploration Program, said in a statement, “We're finding more places where Mars reveals a warmer and wetter planet in its history. This gives us greater incentive to continue seeking evidence of past life on Mars.”

As Opportunity continues to shape our understanding of Mars, one recent discovery by the rover remains unsolved. The Mars "jelly doughnut" rock that suddenly appeared in front of Opportunity has yet to be explained by researchers are hard at work analyzing the rock and its unusual composition.