c ale ▁of ▁their ▁formation . ▁At ▁the ▁current ▁locations ▁it ▁would ▁have ▁taken ▁millions ▁of ▁years ▁for ▁their ▁cores ▁to ▁acc re te . ▁ ▁This ▁means ▁that ▁U ran us ▁and ▁Ne pt une ▁ ▁may ▁have ▁formed ▁closer ▁to ▁the ▁Sun — near ▁or ▁even ▁between ▁Jup iter ▁and ▁Sat urn — and ▁later ▁migr ated ▁or ▁were ▁e ject ed ▁out ward ▁( see ▁Planet ary ▁migration ▁below ). ▁Mot ion ▁in ▁the ▁plan etes imal ▁era ▁was ▁not ▁all ▁in ward ▁toward ▁the ▁Sun ; ▁the ▁St ard ust ▁sample ▁return ▁from ▁Com et ▁Wild ▁ 2 ▁has ▁suggested ▁that ▁materials ▁from ▁the ▁early ▁formation ▁of ▁the ▁Sol ar ▁System ▁migr ated ▁from ▁the ▁war mer ▁inner ▁Sol ar ▁System ▁to ▁the ▁region ▁of ▁the ▁K ui per ▁bel t . ▁ ▁After ▁between ▁three ▁and ▁ten   mill ion ▁years , ▁the ▁young ▁Sun ' s ▁solar ▁wind ▁would ▁have ▁cleared ▁away ▁all ▁the ▁gas ▁and ▁dust ▁in ▁the ▁pro top lan et ary ▁disc , ▁blow ing ▁it ▁into ▁inter stell ar ▁space , ▁thus ▁ending ▁the ▁growth ▁of ▁the ▁plan ets . ▁ ▁Sub sequ ent ▁evolution ▁The ▁plan ets ▁were ▁originally ▁thought ▁to ▁have ▁formed ▁in ▁or ▁near ▁their ▁current ▁or bits . ▁This ▁has ▁been ▁question ed ▁during ▁the ▁last ▁ 2 0 ▁years . ▁Currently , ▁many ▁planet ary ▁scient ists ▁think ▁that ▁the ▁Sol ar ▁System ▁might ▁have ▁looked ▁very ▁different ▁after ▁its ▁initial ▁formation : ▁several ▁objects ▁at ▁least ▁as