Reminds me of a book I just read...it's a ya book by a local Colorado author. YellopJeep will have to give us the title since I can't remember.
BUT...it's about a comet that comes close to the earth. Months later, everyone over the age of 18 is dying from an illness that is linked to the comet. That is when Earth pulls together to put a spaceship together of teenagers to ship them to another planet to save the human race.
Now while we cannot put a spaceship together (but how cool is that?), we can still prepare in other ways. By reading fiction and non-fiction alike, you can pick up new ideas.
While it is a YA book (now become a series) and soon to be published (I had an advance copy), I highly recommend this as a good read.