The census of known planets in other star systems includes a lot of oddballs: jumbo planets that orbit close to their stars, planets that are less dense than Styrofoam, planets that orbit two stars. So far, it doesn't include any planets the size of Earth, although that's likely to change. A space telescope called Kepler is looking for Earth-sized planets orbiting Sun-like stars. But it's also finding lots of other planets. The discoveries will help theorists explain how all planets form -- including our own.
As Kepler scientist Alan Boss explains, it's a process that's just getting started.
BOSS: Right now we have over 500 systems and counting, and I would say if you wanted to do a sort of a baseball scoreboard, the observers' score is 500 and the theorists' score is 0, because theorists really haven't figured out how to explain the formation of our own solar system. We've got lots of good ideas, but until those ideas are tested by comparing them to the 500 other solar systems, which presumably formed by more or less the same process, you can't really claim that you theory has any general relevance.
By the time Kepler finishes up, we'll have a pretty good census of what planets are like in terms of their sizes, masses and orbital distances.... The really key thing here is that these observations are telling us for the first time what the right answer is. Theorists like to look in the back of the book and see what the answer is before they solve the problem. It used to be all the back of the book had was our own solar system. Now when you look in the back of the book you have 500 planetary systems to try and match up. So that's going to be the real challenge for theorists, to try to come up with theories of planet formation which are general enough and inclusive enough to be able to explain the entire menagerie of planets that we're seeing.
Script by Damond Benningfield, Copyright 2010
Production and distribution of this episode made possible in part by a grant from NASA