Star travel is expensive; it costs on the order of a ship’s own mass in equivalent energy to get it up to relativistic speeds. Any culture capable of that will be at least a Kardashev Type I civilization, and most likely a Type II. And the reason they’ll be doing star travel is to work their way up towards Type III. Any sentient creatures that actually get here will be nanotech-based robots, not water-based organisms. They won’t have spacecraft, they’ll be spacecraft. They will be unlikely interested in the carbon-poor mudballs of the inner solar system, but reap abundant carbon from the outer planets and carbonaceous asteroids to build Dyson-sphere-like structures around the orbit of Mercury.
We simply aren’t going to see less sophisticated visitors due to the starship paradox: send a starship out now with all Earth’s current technological resources behind it, and then wait and send one in 50 years with full nanotech. The second one gets there first.
We aren’t going to see any less ambitious visitors due to simple evolution: in a universe where the ultimate meaning of “carbon footprint” is the total mass of the superintelligent diamondoid robots you’ve built, spaceships burning cellulosic ethanol simply aren’t going to be anywhere near the fittest. Indeed, cultures that aren’t inherently aggressive and ambitious aren’t going to put the effort into sending out starships at all. The question is, what are they going to think of us, the thin layer of green slime coating an insignificant rock?
Read the whole thing. Some interesting links, too.