Alien microbes in space above Mars, conceptual illustration. Mars once had a wet climate, which prompts many astronomers to believe that life may have arisen there in the past, and perhaps exists there still. This illustration conceptualises the idea, showing microorganisms floating above Mars. In 1996, NASA announced that they had found evidence for fossilised microorganisms in a meteorite hailing from Mars. However, whether these structures are indeed fossilised life forms - or merely Earth-based contaminants - remains unsettled.