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Jupiter Destroyed 'Super-Earths' In Our Early Solar System
sciencehabit writes: If Jupiter and Saturn hadn't formed where they did—and at the sizes they did—as the disk of dust and gas around our sun coalesced, then our solar system would be a very different and possibly more hostile place, new research suggests (abstract). Computer models reveal that in the solar system's first 3 million years or so, gravitational interactions with Jupiter, Saturn, and the gas in the protoplanetary disk would have driven super-Earth–sized planets closer to the sun and into increasingly elliptical orbits. In such paths, a cascade of collisions would have blasted any orbs present there into ever smaller bits, which in turn would have been slowed by the interplanetary equivalent of atmospheric drag and eventually plunged into the sun. As Jupiter retreated from its closest approach to the sun, it left behind the mostly rocky remnants that later coalesced into our solar system's inner planets, including Earth.
So how come that happened in our solar system, but not in the many other exo-planetary systems that we have found recently/
Selection bias. Our planet detection technology is still very primitive. We have found lots of big, hot planets orbiting very close to stars, not because they are common, but because they are easy to detect.
Easier to Detect. The easiest to detect is great big gas giants nearly the size of their star orbiting very closely (hot gas giants). Those were the first discovered and comprise the majority of systems discovered so far because the bigger the planet and the closer to the star the easier it is to infer with the current detection techniques. We've never actually imaged one of these worlds, we've only inferred their presence for example by rhythmic flickering from a planet passing in front of the star.
As someone (I can't recall who) said, trying to find planets is like trying to see a mosquito in front of a 10,000 watt light bulb from a football field away. In other words is pretty difficult, in fact so difficult we can only find planets through inferred methods, not direct imaging. Unless we can find a way to completely block all the light from the star without blocking anything illuminated by the star and thousands of times more magnification (say a focal length of half the solar system) we aren't going to image a planet like earth. Space is really really big and the distance between stars so great that even when two galaxies collide there is very little chance of two stars impacting.