The problem, as you might have gathered, is that the Milky Way galaxy isn't part of that bunch. Most of its gas has already been used up. And while there's an estimated 1 billion habitable planets in the galaxy, that's a drop in the bucket when the Milky Way holds as many as 400 billion stars. Earth is not only relatively early, it's in an uncrowded cosmic neighborhood. That's disappointing if you were hoping for a Star Trek-like abundance of extraterrestrial life, but it at least puts Earth's loneliness in context.

[Image credit: NASA, ESA, and G. Bacon (STScI)]