I believe that life once existed on Mars. As a scientist, however, I have absolutely NO proof that it ever did. I even have some severe questions about NASA's announcement that micro-fossils had been detected in a martian meteorite.
I keep my beliefs very separate from what I actually consider proved as a scientist. I believe the universe is swarming with life. I believe that most of this life is simple bacteria. I believe that there are 'many' advanced animals in the Milky Way. I believe that the universe is destined to expand forever. The only one of these beliefs I have that I BELIEVE will be proved or disproved in my lifetime is the last one.
Science is NOT about beliefs. Scientists, however, have many beliefs, which is why a 'good' cosmologist can be a devout cristian, jew, moslim, athiest or agnostic. I know cosmologists and astronomers who are all of these. Is this a contradiction? No. Without beliefs, without dreams of how things might be in the big picture, we are diminished as humans.