As the tally for planets beyond the solar system began climbing, a team of scientists noticed something strange. Most of the other systems in the galaxy had planets bigger than Earth orbiting closer to their parent stars than Mercury circles the sun.
"In our solar system planets are pretty widely spread out and there's literally nothing inside of Mercury's orbit," astronomer Gregory Laughlin, with the University of California Santa Cruz, told Discovery News.
"The fact that the default mode of planet formation ... is leading to configurations that are totally unlike our own solar system is something I found really curious. The main feature of our solar system is that the inner part is just missing," he said.
ANALYSIS: Is Jupiter Evil?
Enter the "Grand Tack" theory of our solar system's formation, which suggests that in its infancy, giant Jupiter spiraled inward, swept by the gravitational wake of its own buildup. Like a cosmic bull in a celestial china shop, Jupiter's gravity would have flung asteroids and proto-planets every which way, creating a shooting arcade that could have easily destroyed planets in the region, Laughlin said.
The story would have ended there were it not for Saturn, which evolved somewhat later and ended up with enough gravitational muscle to counteract Jupiter's inward spiral, freeing the giant planet to shift back beyond Mars, or so the Grand Tack theory holds.
ANALYSIS: Has Earth Splattered Life All Over the Solar System?
That left the inner solar system clear for a second-generation of planets to form, Earth among them.
Laughlin and colleagues were less interested in proving Jupiter's navigational prowess than looking at what impacts the migration could have had.
"Anytime a theory says 'Well this happened and then this happened,' you need to be naturally suspicious. I think that is completely, absolutely valid and the right standpoint to take," Laughlin said.
But looking at the consequences of the migration provides a very nice test, he added.