Scientists have concluded from reviewing data of 1976 Mars Viking rovers that bacteria existed on Mars.
The original consensus of scientists has been that the experiment found geological, not biological activity.
But the new study took a different, purely numerical approach.
Researchers took the hard copy Viking Labeled Release data into sets of numbers and analyzed the results for complexity, as living systems are more complicated than non-biological processes.
"The ultimate proof is to take a video of a Martian bacteria. They should send a microscope - watch the bacteria move," said Miller, neuropharmacologist and biologist with the University of Southern California Keck School of Medicine.
"On the basis of what we've done so far, I'd say I'm 99 per cent sure there's life there!"
On the other hand, critics say the method is not yet proven to differentiating between biological and non-biological processes. "On mars we have no way to test the method, while on Earth we can," countered planetary scientist and astrobiologist Christopher McKay, with NASA's Ames Research Center in Moffett Field, Calif.
The research is published online in the International Journal of Aeronautical and Space Sciences.