Complex sentence: It may have an exceptionally large core composed of elements heavier than hydrogen and helium: the initial theoretical models gave the core a mass of 70 times Earth's mass; further refinements suggest 80-110 Earth masses.
Split into simpler sentences: It may have an exceptionally large core composed of elements heavier than hydrogen and helium. The initial theoretical models gave the core a mass of 70 times Earth's mass; further refinements suggest 80-110 Earth masses.