Space colonisation won't get properly going until we have adequate robotics, nanotech, and maybe genetics, for the job of prefabbing complete self-sustaining habitats which utilise only local resources.
"Sufficient unto the task" is likewise tautologous, I suppose. But simply saying "until we have robotics" is absolutely not what I mean. Oh, and we also need AI, which I'd subsumed under robotics.
Using newer and more powerful infrared telescope technology, able to detect brown dwarfs as cool as 150 kelvins out to a distance of 10 light-years from the Sun,[10] results from the Wide-field Infrared Survey Explorer (WISE survey) have not detected Nemesis.[11][12] In 2011, David Morrison, a senior scientist at NASA known for his work in risk assessment of near Earth objects, has written that there is no confidence in the existence of an object like Nemesis, since it should have been detected in infrared sky surveys http://en.wikipedia.org/wiki/Nemesis_%28hypothetical_star%29