▁a ▁bar rier ▁that ▁caused ▁material ▁to ▁accum ulate ▁rapidly ▁at ▁~ 5   AU ▁from ▁the ▁Sun . ▁This ▁excess ▁material ▁co ales ced ▁into ▁a ▁large ▁emb ry o ▁( or ▁core ) ▁on ▁the ▁order ▁of ▁, ▁which ▁began ▁to ▁accum ulate ▁an ▁en velope ▁via ▁acc ret ion ▁of ▁gas ▁from ▁the ▁surrounding ▁disc ▁at ▁an ▁ever - in cre asing ▁rate . ▁ ▁Once ▁the ▁en velope ▁mass ▁became ▁about ▁equal ▁to ▁the ▁solid ▁core ▁mass , ▁growth ▁proceeded ▁very ▁rapidly , ▁reaching ▁about ▁ 1 5 0   E arth ▁masses ▁~ 1 0 5   year s ▁there after ▁and ▁finally ▁to pping ▁out ▁at ▁. ▁ ▁Sat urn ▁may ▁o we ▁its ▁substantial ly ▁lower ▁mass ▁simply ▁to ▁having ▁formed ▁a ▁few ▁million ▁years ▁after ▁Jup iter , ▁when ▁there ▁was ▁less ▁gas ▁available ▁to ▁consume . ▁ ▁T ▁Ta uri ▁stars ▁like ▁the ▁young ▁Sun ▁have ▁far ▁stronger ▁stell ar ▁wind s ▁than ▁more ▁stable , ▁older ▁stars . ▁U ran us ▁and ▁Ne pt une ▁are ▁thought ▁to ▁have ▁formed ▁after ▁Jup iter ▁and ▁Sat urn ▁did , ▁when ▁the ▁strong ▁solar ▁wind ▁had ▁blow n ▁away ▁much ▁of ▁the ▁disc ▁material . ▁As ▁a ▁result , ▁those ▁plan ets ▁accum ulated ▁little ▁hydro gen ▁and ▁hel ium — not ▁more ▁than ▁ ▁each . ▁U ran us ▁and ▁Ne pt une ▁are ▁sometimes ▁referred ▁to ▁as ▁failed ▁cores . ▁The ▁main ▁problem ▁with ▁formation ▁theories ▁for ▁these ▁plan ets ▁is ▁the ▁times