Jupiter cleared path for solar system.

• Position: Solar System

Jupiter may have swept through the early solar system like a wrecking ball, destroying a first generation of inner planets before retreating into its current orbit, according to a study from the University of California, Santa Cruz. The findings help explain why our solar system is so different from the hundreds of other planetary systems that astronomers have discovered in recent years.

"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 Gregory Laughlin, professor and chair of astronomy and astrophysics. '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."

The research explains not only the "gaping hole" in our inner solar system, but certain characteristics of Earth and the other inner rocky planets, which would have formed later than the outer planets from a depleted supply of planet-forming material.

Laughlin and coauthor Konstantin Batygin, assistant professor of planetary science at the California Institute of Technology, Pasadena, explored the implications of a leading scenario for the formation of Jupiter and Saturn. In that scenario, proposed by another team of astronomers in 2011 and known as the "Grand Tack," Jupiter first migrated inward toward the sun until the formation of Saturn caused it to reverse course and & migrate outward to its current position. Batygin performed numerical calculations to see what would happen if a set of rocky planets with close-in orbits had formed prior to Jupiter's inward migration.

At that time, it is plausible that rocky planets with deep atmospheres would have been forming close to the sun from a dense disk of gas and dust on their way to becoming typical "super-Earths" like so many of the exoplanets astronomers have found around other stars. As Jupiter moved inward, however, gravitational perturbations from the giant planet would have swept the inner planets (and smaller planetesimals and asteroids) into close-knit, overlapping orbits, setting off a series of collisions that smashed all the nascent planets into pieces.

"Ifs the same thing we worry about if satellites were to be destroyed in low-Earth orbit. Their fragments would start smashing into other satellites and...