In recent years, scientists have discovered more than 1000 exoplanets orbiting stars in our galaxy, many of which are part of multiple planet systems. The majority of these alien solar systems are quite unlike our own, with a few planets several times larger than the Earth ('super-Earths') orbiting closer to their host star than Mercury is to the Sun.
"Now that we can look at our own Solar System in the context of all these other planetary systems, one of the most interesting features is the absence of planets inside the orbit of Mercury," says Dr Gregory Laughlin, astrophysicist at the University of California, Santa Cruz. "The standard issue planetary system in our galaxy seems to be a set of super-Earths with alarmingly short orbital periods. Our Solar System is looking increasingly like an oddball."
Laughlin and his colleague Dr Konstantin Batygin wondered whether Jupiter's early development might have been responsible for our unusual Solar System. They looked at a scenario that was first suggested in 2011, in which Jupiter migrates inwards toward the Sun, but then changes tack, pulled back by Saturn's gravitational force to its current position.
The researchers calculated what would have happened if a set of rocky planets had developed close to the Sun by the time Jupiter migrated, similar to those super-Earths we see in many other solar systems.
Their calculations showed that the wandering Jupiter would have swept the inner planets into overlapping orbits, putting them on a collision course which would have seen them blown to smithereens. This would have cleared the way for the planets that eventually formed our inner Solar System - Mercury, Venus, Earth and Mars.
"It's the same thing we worry about if satellites were to be destroyed in low-Earth orbit," says Laughlin. "Their fragments would start smashing into other satellites and you'd risk a chain reaction of collisions. Our work indicates that Jupiter would have created just such a collisional cascade in the inner Solar System."
So maybe we owe our very existence to the wanderings of that great gas giant.
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