Mars is out; the moon is in. And this time, we may be going there to stay. On March 24, NASA administrator Jared Isaacman announced new plans to build a " sustained human presence " on the moon, complete with a permanent lunar base. Construction of humanity's new home away from Earth could begin as soon as 2027, Isaacman said. It's an exciting prospect — but scientists say lunar colonization won't be as simple as packing up and lifting off. The moon's environment is harsh: think razor-sharp, electrified dust and a constant stream of radioactive particles travelling at light speed. Scientists still aren't sure how this increased dose of cosmic radiation, coupled with the moon's weaker gravitational pull, relative to Earth, will affect the human body in the medium- to long-term. And then there's technological feasibility: Where will astronauts live, and with what resources? At the moment, these big questions are still awaiting answers that may not arrive in time for NASA and Musk's proposed plans.…