Who can say there is not a deadly virus on Mars which we can not determine? We can't bring back samples from Mars. It would kill all life here just like it may have only Mars. Anylize the dirt there and send back the results. There are unfathomable contagians we can't recognize with our equipment. The space craft and all equipment should stay there just to be on the safe side. The only race we are in is not a Mars contest but the human race.