Alien life exists, 100%.
Alien life existed on mars, 90%
Alien life still exists on mars, 80%.
Scientists are currently estimating we will find alien life within the next 20 years or so.
Microbes are super resilient, we've come to find that the protein strands which preclude more complex molecules self-establish pretty easy, and we've found quite a few earth-like planets recently.
Alien microbial life is almost certainly beneath the surface of mars, probably elsewhere in our solar system.