In the blurb found here, Phil Berardelli reports "New models suggest that as many as one-third of the solar systems in the galactic neighborhood might contain terrestrial planets with oceans of water that could harbor life."
While original thoughts on the whole "hot Jupiter" thing seemed to indicate that solar systems with close-in gas giants would either suck up or eject all the good rocky stuff from a solar system, the latest thinking goes against that grain.
But "the new models indicate these early ideas were probably wrong," says planetary scientist Sean Raymond of the University of Colorado, Boulder. Reporting in today's issue of Science, Raymond and colleagues say they ran simulations lasting more than 8 months each on more than a dozen desktop computers. They observed how nascent solar systems evolved over about 200 million years, basing the initial conditions on current theories of how planets formed in our own solar system. The researchers found that when gas giants migrate, they fling lots of rocky debris away from the star and into the habitable zone, where liquid water can exist on a planet's surface. There, the debris frequently coalesces into Earth-sized planets.
Well, that's pretty cool. Combine that with a buncha comets on water delivery duty, and presto chango - you got a little earth thing goin' on. A little abiogenesis and/or Incompetent Designer, and there ya' go. Trans-gender Purple Octopus Aliens for us to hang out with.
The abstract can be found here.