More Than You Wanted To Know...

... About extrasolar planets.

Reading various news sources about the newest small planet found near the center of the galaxy reminded me of something. In spiral galaxies like our own, there is a "habitable zone" around the centre of the galaxy in which life-supporting planets can form. Further towards the centre of the galaxy, and the gravitational tug of war plays havoc with planetary formation and probably ruins the chance for life. Further out, however, and stars are too poor in heavier elements for planets to form.

It's analogous to the habitable zone around the sun, which Earth is privliged to sit nicely in the middle.

Anyway, this most recently discovered star is pretty much on the inner limit of the habitable zone. So far, the most recent theories predict that about 5-10% of stars lie in the habitable zone, meaning approximately 10-20 billion stars are potential homes for other life.

Or, to state it more cynically, 180-190 billion stars are inimically hostile to life as we know it.

As for the question of actual life out there somewhere, I'm more or less agnostic. Gerard K O'Neill summed up our situation pretty well. At the end of his book 2084, he wrote that destroying human civlization would be ridiculously easy for any race capable of interstellar flight. The mere fact that we exist therefore means that either a) The aliens are there, but they're benign, or b) they aren't there at all.

Either way, it looks good for us.