Simplify the following text for a Grade 6 native English-speaking person.
Original: Mercury 's density is the second highest in the Solar System at 5.427 g\/cm3 , only slightly less than Earthâ s density of 5.515 g\/cm3 .
Simplified: Mercury 's density is the second highest in the Solar System at 5.427 g\/cm Â , only a little bit less than Earthâ s.