There’s something about our solar system that appears to be unusual. For some reason, most of our bigger planets are far away from our host star, while closer in are smaller, rocky worlds, including Earth itself. This is not the case for many extra solar systems that have been discovered. So-called “hot Jupiters” — huge gas giant planets that nestle close to their star — have been found in a few examples. In other instances, planets slightly bigger than Earth are so close to their stars as to be uninhabitable. Did our solar system once look like this, or did it start out somewhat differently? As nobody was around to witness the forming of our solar system some 4.5 billion years ago, computer simulation is the next best means to unraveling this mystery. A new series of simulation scenarios suggests that Jupiter may have formed in a distant orbit, but temporarily invaded the orbital neighborhood of the present Earth before migrating back out.