Simplify the following text for a Grade 5 native English-speaking person.
Original: Jupiter 's core is thought to be approximately 12 times the mass of Earth ( 3 % of Jupiter 's total mass ) , and the exoplanet HD 149026 b is thought to have a core approximately 70 times the mass of Earth .
Simplified: Jupiter 's core is estimated to be 12 times the mass of the Earth 's .