Milky Way Stuffed With an Estimated 50 Billion Alien Worlds

astroengine writes "Using data extrapolated from the early Kepler observations of 1,235 candidate exoplanets, mission scientists have placed an estimate on the number of alien worlds there are in our galaxy. There are thought to be 50 billion exoplanets, 500 million of which are probably orbiting within their stars' habitable zones."

Re:Only 50 billion?

[jgoemat]

Kepler is only looking at Sun-like stars, which only account for 13% of the stars in our galaxy. Also the mission has only been going on for two years and they need at least two transits to say they might have found a planet, so this wouldn't count planets much further away from their star than Earth is from Sol.

Re:Oblig.

[julesh]

Not to mention this whole "habitable zone" thing is a load of crap IMHO. I mean what are the odds that some alien race is gonna come out just like us and therefor need the exact same conditions as us?

Habitable zone === possibility of liquid water on open surface. This is much broader than the exact same conditions we require, and as we've had theorists thinking for a long time about possible life chemistries that are different from our own, and most still think that water-based life is the most likely to occur, it seems a reasonable starting point.

We have already detected the possibility of liquid water on Europa IIRC, and that is pretty damned far from the "habitable zone" so who is to say there aren't plenty of creatures living on worlds farther out?

Europa is a pretty unusual situation. It also has a few serious disadvantages that may make it less likely that life would occur on it than a typical "habitable zone" rocky planet, some of which are likely to happen anywhere a similar feature occurs. The biggest is that it's quite small, which reduces the likelihood of a life-starting reaction occuring there. It's energy-starved in comparison to a planet with a warm surface, which also makes the likelihood of a life-starting reaction lower. Both of these issues are likely to apply to Europa-like moons in other star systems.