Density of a planet or moon

If we know the mass M and radius R of a planet or moon, we can compute its density, which is its mass divided by its volume. Here is the formula for the density of a sphere:

If you divide by the same formula for the density of some standard object like the earth or our moon, using M₀ and R₀ for the mass and radius of the standard object, you have

Thus we get

This formula is nice and simple.

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