The evidence for life on Mars, now or in the past, continues to be elusive though the evidence is tantalizing. Though we have evidence for water in the past on Mars (and water is necessary for life as we know it) no probes nor satellites nor Rovers have come up with unequivocal evidence for life on Mars. In the 70’s the Viking mission did experiments looking for living organisms by looking for the results of metabolism in soil samples. These were faulted because the results could have been the result of geochemical reactions in the soil sample. Methane, which exists on Earth, is evidence of metabolism by bacteria, cows, and termites, has been detected sporadically in the Mars atmosphere by spectroscopic analysis from Earth, satellites, and Curiosity. However, it is problematic for many reasons but— as it has not been determined as NOT to be from living organisms—leaves hope. Curiosity’s mission is not to look for life so it is not the optimal instrument to accomplish this task. There is an instrument on Earth, destined to go to Mars (but not yet scheduled) that is far more sensitive than the instruments currently in place. NASA also, because of claims like life on Mars, needs unequivocal proof, has decided a sample return mission with an analysis in Earth laboratories is the only way to make certain of the results. That is not on the schedule for anytime soon.
So where does this leave us? Tantalizing evidence for life on Mars but good evidence for water in Mars’ past. Why is this important? We would like to know if life had two (or more) independent origins; on Earth and Mars. If so, it would suggest that life is not so difficult to start and that might suggest that if it occurred on Earth AND Mars that it probably occurred elsewhere in the Universe. Even if it did not occur on Earth and Mars it could have occurred elsewhere given the huge number of planets. Mars is more accessible than planets in the Universe so that is where we are looking. Also, we maybe the original Martians if life began on Mars and was transferred by meteorite to Earth. Genome studies of organisms brought back from Mars would help us understand that.