To that end, the magazine asked Conley a lot about Mars, where NASA has deployed exploratory spacecraft and robots since the mid-1970s to search for clues about the existence of water, prospects for habitability and any existence of life. The earliest missions, part of NASA's Viking program, included meticulous steps to not sully the Martian landscape, she said.

"The landers," Conley explained, "were packaged and put inside a bioshield and baked in an oven to kill all organisms - a 'full-system sterilization,' we call it. . . . We needed to protect the life-detection instruments and protect the Mars environment in case it turned out to be habitable to Earth life."

Today, rovers operate where it's believed water once existed, gathering imagery, analyzing the environment and beaming that data back to Earth. And as scientists' understanding of the Red Planet evolves, so do the questions facing those working to send people there in the coming decades.

"Will the humans be alive by the time they get to Mars?" Conley asked in 2014. "If they die on Mars, are they then contaminating the surface?" That could interfere with future research, she said.