Simplify the following text for a Grade 5 native English-speaking person.
Original: The composition and mass of Metis are not known , but assuming that its mean density is like that of Amalthea ( ~ 0.86 g\/cm Â ) , its mass can be estimated as ~ 7 Ã -- 1016 kg .
Simplified: The bulk composition and mass of Metis are not known , but assuming that its mean density is like that of Amalthea ( ~ 0.86 g\/cm Â ) , its mass can be estimated as ~ 3.6 Ã -- 1016 kg .