A key part of the search focused on organics, a quest that has led to the surprising discovery that organic matter may be widely distributed on Mars.
"To me this is the biggest take-home message. Four years ago, we would never have said this," Eigenbrode said.
Scientists don't know the source of the organics, nor how the material has managed to survive in the harsh radioactive environment on Mars. It was found in samples drilled out from rocks and chemically analyzed.
Whether biological or geologic in origin, a rich supply of organics has implications not only in the search for past life, but also in supporting future endeavors, such as farming.
"That organic matter could be really important," Eigenbrode said. "The door is really open here to an expanded habitability potential."
In related research, California Institute of Technology geologist John Grotzinger, said Curiosity, which has been slowly making its way up Mount Sharp, has found multiple examples of primary igneous minerals being altered.