Formation and evolution of the Solar System timescale of their formation. At the current locations it would have taken millions of years for their cores to accrete. This means that Uranus and Neptune may have formed closer to the Sun—near or even between Jupiter and Saturn—and later migrated or were ejected outward (see Planetary migration below). Motion in the planetesimal era was not all inward toward the Sun; the "Stardust" sample return from Comet Wild 2 has suggested that materials from the early formation of the Solar System migrated from the warmer inner Solar System to the region of the Kuiper belt. After between three and ten
Planet V Sun after entering the ν secular resonance. As an initial test of the Planet V hypothesis, Chambers and Lissauer conducted 36 computer simulations of the Solar System with an additional terrestrial planet. A variety of parameters were used to determine the impacts of Planet V's initial orbit and mass. The mean time at which Planet V was lost was found to increase from 100 Myr to 400 Myr as its initial semi-major axis was increased from 1.8 to 1.9 AU. Results consistent with the current Solar System were most common with a 0.25 Mars mass Planet V. In cases with