Pictures or it doesn’t exist....
If it were big enough and rocky enough....
It may be big enough to generate enough internal heat to be habitable, as long as the atmosphere isn’t too thin or thick it could even have life!
But that is being really really hopeful!
Until proven otherwise, belief that life exists elsewhere in this solar system remains the only secularly accepted religion in Western culture (with the possible exception of Buddhism and perhaps Islam).
Every new discovery that we make in astrophysics increases the odds against the possibility of life (and certainly intelligent life) existing anywhere else in the universe.
I think the orbits of the known dwarf planets are quite convincing that there is another large planet. The predicted orbit in the following image is orange. All the other orbits are of known dwarf planets.
There is something causing the orbits to bunch up on one side of the solar system.
http://mediaassets.caltech.edu/documents/45-p9_kbo_extras_orbits_2_.jpg
