It's not a question of whether or not there is life on that planet. Its the question of if we even know if there is or isn't life on that planet. The truth is, nobody knows, and there are several points that support it, and several points that do not. In the end, it's up to the person pondering this dilemma, to decide whether there is life, or not.
There is a habitable zone in each solar system in which there may be Earth-like planets. The possible ninth planet in our solar system is not in the habitable zone, so it won't have life on it. However, there are millions of other solar systems out there, so chances are, a lot of them have Earth-like planets that have life on them. There are probably plenty of human-like species in the universe, who are at different stages of evolution than we are.
No, scientists will not find life on other planets, because it is too hard for other planets to sustain life. It took a very special combination of conditions on Earth in order to sustain life. There is no way that a person could live on Neptune or Mercury or any other place. There is just no way for life to live.
There won't be any life on that planet, only ice. If it's further than the former planet Pluto, then it will have a harsher environment. Life as we know it cannot exist in such conditions, so if scientists someday do find a life form on that planet, I don't think they would be able to agree if it was life at all.