Among the most puzzling of the new types of giant planet to have been discovered orbiting stars beyond our Solar System are the ‘hot Jupiters’ – gas giants with the mass of Jupiter or more that sit very close to their stars – sometimes completing an orbit in just a few days or even hours. In some cases, these planets are actually evaporating in the heat, leaving wakes of gas trailing behind them as they move.
According to our understanding of the way that gas giants form, the material needed to create them was never present this close to their stars, so instead they must have started much farther out, and then migrated inwards on a spiral path. Computer models suggest that something like this also happened to Jupiter early in the history of our own Solar System, but that it was ‘saved’ and restored to its current position by interaction with Saturn, before it could wreak havoc on the inner planets.
Other planetary systems may not have been so lucky, and there’s even some evidence of stars that have recently swallowed their unfortunate planets altogether.