What provided the necessary mass boost for the cores of Jupiter and Saturn to rapidly accrete hydrogen and helium gas?

Answer

The abundance of solid, frozen hydrogen compounds (ices).

The availability of abundant ices beyond the frost line allowed proto-planets to build cores significantly more massive than those in the inner system, enabling them to reach the critical mass needed to capture the surrounding lightweight gas.

What provided the necessary mass boost for the cores of Jupiter and Saturn to rapidly accrete hydrogen and helium gas?
Spaceastronomycompositionsolar systemformationcomponentssolar nebulaPlanetary Formation