This Is What Extraterrestrial Life Would Look Like

3. On Interstellar Generation Ships

Stepping outside that pesky box for a second, there's no reason why aliens should be living around a star at all. A Generation Ship, or Interstellar Ark or whatever you want to call it, is basically a starship that travels in open space, either on its way to a specific location such as another habitable planet, or just drifting through space. In the absence of faster-than-light travel, these kinds of arks are pretty much the only conceivable way anyone could explore the galaxy - the Milky Way is 100,000 light years across and so would take millennia to explore just a small part of it, even at light speed. The generation ship would be crewed by successive generations of a civilisation and would essentially become a huge, roving planet. For a civilisation to thrive on a generation ship, it would have to be a self-sustaining habitat with no need for external input. The society itself would have to be extraordinarily stable as mutiny in deep space is probably not a pretty sight. It's also entirely possible that a ship like this could kick-start a whole new branch of evolution, meaning that if humans ever embarked on a round-the-galaxy mission in one, they might not be humans by the time they got back.