The scientist have determined our planet is losing its atmosphere. We wont have more than a few generations. Our technology is advanced enough that we can transport a sizable population to the third planet and will begin soon. None of the other bodies in system can survive our species. Hopefully we can develop star travel and not have our options so limited again in the future. The Human race might just be clever enough to avoid extinction, if we don't forget who we are ... survivors helping one another.