Universe Today
An artist's impression of the different configurations of asteroid belts that could occur. Image credit: NASA/ESA/A. Feild, STScI
"Our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet," said Martin, the study's lead author. "Our study suggests that our solar system may be rather special."
A Jupiter-sized world migrates slowly inward, disrupting the asteroid belt before it can really form. All the potential asteroids are consumed or flung out into deep space. A potential Earthlike world is deprived of the chemicals (and catastrophic incentive) to evolve complex lifeforms. That's bad
No large Jupiter-sized world forms at all, allowing the solar system to create a massive asteroid belt. Material from this enormous asteroid belt would be too punishing to Earthlike worlds for complex life to stand a chance. Also bad.
A Jupiter-sized world forms in the outer solar system, and only moves in a little, preventing an overly large asteroid belt from forming. There are still enough asteroids out there to seed an Earthlike world with chemicals and evolutionary encouragement, but not enough to set its progress back. That's us!