Scientist even doubt that a colony can be put on the Moon due to the onset of bone loss and the exposure to radiation.That's been a suspicion for a long while; Asimov included that in one of his short stories, prior to the lunar landings.
Yep. It's looking way bad for Mars too, which has no rotating core like the Earth and therefore no magnetosphere to block incoming radiation.
When asked where he would choose to land on Mars, former astronaut and senator John Glenn replied "In the highlands where there are caves so I can get shelter from the radiation."
Dude knows the deal.
If we're ever going to set up a colony on the Moon or Mars, I'm convinced that we're going to have to build super-sophisticated robots that we can operate from earth in order to make subterranean shelters for us when we get there. I think whatever humans travel to Mars in (if we ever do) it's going to have to duplicate the effect of Earth's magnetosphere and do it for years albeit on a much smaller scale. Essentially, the ship will need what sci-fi mavens have come to refer to as "shields." I can't even begin to imagine the power necessary for that.