When I was a kid, I loved poetry and science fiction, and once when someone asked me what I wanted to be when I grew up, I told them, the first poet laureate of Mars. Confession: that's still my dream job.
I checked out an article on the fatwa. If I understand it correctly, the idea is that the inherent risks of planetary relocation are far greater than its potential benefits. If you willingly take on such a risk, that's the same thing as committing suicide. So anyone who dies on a mission to Mars is going to Hell, because suicide won't be forgiven, and they would have effectively committed suicide. The fatwa is then justified because it saves people from eternal damnation.
I personally think it's obvious that the people going to colonize Mars aren't thrill seekers, but people who will have been carefully selected because they believe in the value of the mission, and because of their value to the mission. In other words, they believe the sacrifice is justified because the potential value of the mission to humanity is greater than the value of their individual life. I actually don't totally understand why Muslims would have a problem with that -- I think it's obvious that someone could take on that task for selfless reasons and with a clean conscience.
I don't see how this could possibly confront the beliefs of Christians. Christian missionaries have always done heaps of risky stuff to serve the needs, both spiritual and material, of others. I wouldn't be surprised if Christians try to get a seat on the rocket as a chaplin to serve the spiritual needs of the crew.