Proteus is probably not an original body that formed with Neptune. It could have accreted later from the debris formed when the largest Neptunian satellite, Triton, was captured.
proteus IS prObaBlY Not an oRIgInAl boDy thAt Formed wIth nepTune. it Could haVE accreTED LaTer fRom ThE dEbrIS foRmED when The lARgest NePTUniaN SatellITe, triton, Was CAPturEd.