In article ,
Szczepan Bialek wrote:

The density of the Earth is 5.52

The Mars has 3.95 and The Moon 3.34

The density of the moon is very similar to that of the earth's mantle,
which is one piece of evidence for the moon having been formed in a
collision between the earth and some other body. The earth retained
its dense metal core and the moon was formed from part of the lighter
outer material.

Mars's density may be due to its having a smaller core than the earth.

-- Richard