Try to get your hands on a copy of National Geographic's November ('16) edition, "Race to The Red Planet". It's a fascinating read.
In a nutshell, colonizing other star systems (let alone our own solar system) is going to be challenging.
Here's the straight skinny....human beings, as we are currently constructed are not made to combat the extreme rigors of extended space travel. As we already know, Zero Gravity wreaks havoc on our bodies over long periods of time.
It's one thing to be 250+ miles from the surface of the earth (ie: the International Space Station) however once we get outside of the "safety shield" the earth's electro-magnetic field provides, we'll need to figure out how to contend with exposure to varied levels of hazardous cosmic rays and other space radiation.
This is where genetic scientists come in. If we're to send manned missions into deep space we're going to need to create genetically altered human beings. Now....doesn't that just open up a whole new can of worms for the politicians and theologians to debate, hmmm?