Elon Musk, the billionaire founder and CEO of the private spaceflight company SpaceX, wants to help establish a Mars colony of up to 80,000 people by ferrying explorers to the Red Planet for perhaps $500,000 a trip.
(...) we've put all our eggs in one basket. If we were on many worlds and were to mess up down here, there's a way for the human species to continue. I don't for a moment propose that the Earth is a disposable planet, and we have to put enormous efforts into making sure we don't muss up down here. But there is a chance.
OK, makes sense. If we assume the AI to be perfectly rational, it would probably give exterminating humanity out of Earth high priority, exactly because there is a chance of them building another AI.
However, to wipe out humanity from the Earth, the AI does not have to be very smart. One virus, well designed and well distributed, could do the job. An AI with some bugs could still be capable to make it... and then fail to properly arrange the space attack, or destroy itself by wrong self-modification.