Wandering Jupiter Cleared Path for our Unusual 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 new study published March 23 in Proceedings of the National Academy of Sciences. 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," said Gregory Laughlin, professor and chair of astronomy and astrophysics at UC Santa Cruz and coauthor of the paper. "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 new paper explains not only the "gaping hole" in our inner solar system, he said, but also 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 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, who first worked with Laughlin as an undergraduate at UC Santa Cruz and is now an assistant professor of planetary science at the California Institute of Technology, 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.
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► Image: Jupiter is thought to have migrated inward toward the sun before retreating to its current position in the solar system.
Credit: NASA/Cassini