Research offers clues about the timing of Jupiter's formation http://phys.org/news/2016-12-clues-jupiter-formation.html
A peculiar class of meteorites has offered scientists new clues about when the planet Jupiter took shape and wandered through the solar system.
Scientists have theorized for years now that Jupiter probably was not always in its current orbit, which is about five astronomical units from
the sun (Earth's distance from the sun is one astronomical unit). One line of evidence suggesting a Jovian migration deals with the size of Mars.
Mars is much smaller than planetary accretion models predict. One explanation for that is that Jupiter once orbited much closer to the sun than
it does now. During that time, it would have swept up much of the material needed to create supersized Mars.
But while most scientists agree that giant planets migrate, the timing of Jupiter's formation and migration has been a mystery.
That's where the meteorites come in.
Meteorites known as CB chondrites were formed as objects in the early solar system—most likely in the present-day asteroid belt—slammed into each
other with incredible speed. This new study, published in the journal Science Advances, used computer simulations to show that Jupiter's immense
gravity would have provided the right conditions for these hypervelocity impacts to occur. That in turn suggests that Jupiter was near its current
size and sitting somewhere near the asteroid belt when the CB chondrules were formed, which was about 5 million years after formation of the first
solar system solids.