NEO Impacts
I believe we need to colonize elsewhere just on the pretense of an Earth ELE (Extincton level Event) from an NEO, which I believe is inevitable.
And I do believe, to this day that Apohis 2004 is a threat in the 2036 time frame. The Gov just doesn't know enough yet to say this rock will clear earth, and we won't for a good 10 years yet. I say the Gov is working behind the scenes on this possible threat.
IMHO....