In the search for life on Mars, are robots nearing their limits?

Curiosity and the upcoming Mars 2020 rover will continue the search for indirect signs of microbial life on Mars, but some scientists suggest it might take a human touch to uncover conclusive evidence.

Is there – or was there ever – life on Mars? NASA has spent decades investigating the question with orbiters and rovers, including its upcoming Mars 2020 rover, but at least one scientist suspects he already knows the answer.

According to Gibert Levin, NASA probably detected microbial life on Mars in 1976.

Dr. Levin was one of the scientists involved with the Viking lander, whose biological experiments gave conflicting results when samples tested positive for metabolism but negative for organic molecules. Scientists at the time agreed that what looked like biological signs must have resulted instead from natural processes, but after decades of follow-up research recreating the Martian experiments in hostile landscapes such as Antarctica and the Atacama Desert, combined with a better understanding of Mars as well as the durability of life on Earth, Levin has a different hypothesis:

The unreliable organic molecule experiment was the one that failed, and the metabolism detection succeeded.

The continued debate surrounding the interpretation of a four-decade-old experiment highlights the challenges of looking for life, or its fossilized remains, with indirect experiments conducted by robots a world away.

(Image Credit: NASA)