I believe a survey of planetary systems showed that the gas giants were more common closer to the stars (hot Jupiters), and they tended to eject the rocky inner

I believe a survey of planetary systems showed that the gas giants were more common closer to the stars (hot Jupiters), and they tended to eject the rocky inner planets. Our solar system might be exceptional because of Saturn preventing Jupiter from migrating inward. Also the collision of Earth with the other body that eventually formed the Moon, as violent and destructive as it was when it happened, may been a big reason why the Earth is tectonically active (which also is the reason for the magnetic field, which helps keep our atmosphere intact) and the presence of the Moon also gives us tidal forces which may have been necessary for abiogenesis, The collision of such a large object at the right time of planetary evolution may have been a low probability event. OTOH, alternatives have bene proposed. The moons of the "hot Jupiters" could get similar benefits as the Moon and the remnants of the collision gives Earth In particular, it is known that the moons of Jupiter experience substantial tidal forces.