[Magnum44]

What the article doesn't state though is that planetary systems without Jupiter like outer planets cannot support advanced life either, because the large Jupiter like gas giants are required to keep catastrophic meteors from impacting any life bearing planets in the habital zone.

Huh? What space science book did you get this from? I disagree with your statement, though as shoemaker-levy showed us, an outer planet can capture an occasional comet/asteroid.

[donh]

What the article doesn't state though is that planetary systems without Jupiter like outer planets cannot support advanced life either, because the large Jupiter like gas giants are required to keep catastrophic meteors from impacting any life bearing planets in the habital zone.

Huh? What space science book did you get this from? I disagree with your statement, though as shoemaker-levy showed us, an outer planet can capture an occasional comet/asteroid.

I don't think you're getting the point. A large jupiter-like planet serves as a vacuum sweeper to mop up all the loose chunks of rock in accentric orbits that might eventually slam into a life-bearing inner planet. Leaving only chunks of rock whose orbits are similarly close to circular, such as ours. (And therefore, a great deal less likely to hit us.) This has the effect of greatly reducing the impact hazards on the road. Considering that we came very close to losing all of life on this planet 5 times from known impacts, this is not an inconsiderable service, which must be counted as a major element in assessing the probability of life on a given planet.