Why do We Go to the Stars?
If our Sun or a nearby star were about to go supernova, a major program of interstellar spaceflight might suddenly become attractive, In fact, the discovery that the galactic core was imminently to explode might generate very serious interest in transgalactic or intergalactic spaceflight. Such cosmic violence occurs sufficiently often that nomadic spacefaring civilizations may not be uncommon.
However there may be many other motivations to go to the stars: an emerging technical civilization, after exploring its home planetary system and developing interstellar spaceflight, would tentatively begin exploring the nearby stars.
Some of these stars would have no suitable planets – perhaps they would all tiny asteroids or giant gas worlds. Others would carry an entourage of suitable planets, but some would be already inhabited, or the atmosphere would be poisonous or the climate uncomfortable.
In many cases the colonists might have to change –or as we would parochially say, terraform – a world to make it adequately clement.
The re-engineering of a planet will take time, but suitable world would be found and colonized.
The utilization of planetary resources so that new interstellar spacecraft could be constructed locally would be a slow process. Eventually a second-generation mission of exploration and colonization would take off toward stars where no one had yet been. And in this way a civilization might slowly wend its way like a vine among the worlds.
It is possible that at some later time with third and higher orders of colonies developing new worlds, another independent expanding civilization would be discovered.
Very likely mutual contact would already have been made by radio or other remote means. The new arrivals might be a different sort of colonial society.
Conceivable two expanding civilizations with different planetary requirements would ignore each other, their filigree patterns of expansion intertwining, but not conflicting. They might cooperate in the exploration of a province of the Galaxy. Even nearby civilizations could spend millions of years in such separate or joint colonial ventures without ever stumbling upon our obscure solar system.
A million years is a very long period of time, but we could manage… (Cosmos by Carl Sagan). Image: © Megan Jorgensen