Proof of life on Mars? is it possible?

For as long as mankind has been observing the heavens, we have been fascinated by the possibility that other worlds - much like Earth - might contain living organisms. While our visits to the moon have taught us that it is completely barren and uninhabited, other planets in our solar system show much potential. Venus, for example, could harbor life in its cloud layer. Europa and Enceladus could be teeming with life in a subsurface ocean of liquid water. Even Titan's liquid hydrocarbon lakes are a fascinating place to search for exotic microbes.