Complex sentence: For example, 22 Kalliope has an accurately known density that is far too low for a solid metallic object or even a metal rubble pile: a rubble pile of iron-nickel metal would need about 70% porosity which is inconsistent with packing considerations.
Split into simpler sentences: For example, 22 Kalliope has an accurately known density that is far too low for a solid metallic object or even a metal rubble pile. A rubble pile of iron-nickel metal would need about 70% porosity which is inconsistent with packing considerations.