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
Hydrus 10180, which has seven planets, plus possibly an additional two for a total of nine—as of 2012 more than any other system to date, including the Solar System. Lying around from the Earth, it has an apparent magnitude of 7.33. GJ 3021 is a solar twin—a star very like our own Sun—around 57 light-years distant with a spectral type G8V and magnitude of 6.7. It has a Jovian planet companion (GJ 3021 b). Orbiting about 0.5 AU from its sun, it has a minimum mass 3.37 times that of Jupiter and a period of around 133 days. The system is