Second mars has a weak magnetic field, unlike earth being protected by its huge magnetic field. mars has a very small and weak one.
having a magnetic field protects us from solar flares and solar radiation sun produces. and when mars got hit by a solar radiation even with
the most advance protection agains radiation we have it will be useless resulting to instant death.
Doesn't Mars have some areas that are better protected than others? I think the idea was that they were going to use one of those to settle in since it provided adequate protection.