30 Billion Earth Sized Planets?
Tha_Chaotic_1 writes "The BBC is running a story about a prediction that there are around 30 billion earthlike planets in the universe. This comes following the discovery of the 100th gas giant outside our solar system. Optimistic?"
I think this number is a bit high. I'm not sure they've taken into account that solar systems too close to the center of the galaxy due to the "galactic doughnut" effect. Anything to close to the center of the galaxy, in the doughnut hole, would not be habitable due to excess bombardment of gamma-rays.
Looks like they *think* that they've poked around in a 100 light year radius of earth. Given the extremely poor precision in which distances are measured this may be a bit optimistic.
Also from the article:
And if stellar statistics gathered in our local region of space are applied to our galaxy of 300 billion stars, then there may be 30 billion Jupiter-like worlds and perhaps as many Earth-like worlds as well.
Since our universe is not uniform this may be an abuse of statistics. They've only looked at one very small corner. This is a heck of a Monte-Carlo simulation, though!
There's also a theory that says that you may well need to have at least one gas giant further out from your star to help deflect space schmutz from wiping your species out too early. Since we have 4 very large planets further out from our planet, we've got a lot of gravity wells helping to keep the inner system cleaner than it would normally be. Then again, this may be a rather common configuration - if a star forms and a gas giant forms, then the eddys between the forming star and forming gas giant may just be what turns into a smaller planet. Where's a Wayback Machine when you need one? *sigh*