Is it simple Math or something else?

Grandpa with his mischievous smile said:

"If zero belongs to One

And two belongs to Four

Twenty seven belongs to Seven

Then what belongs to Three?"

Hint

When I could not guess, I asked for a clue. He just smiled and said:

"Think Son"

ONE

Explanation

Counting from the centre of the solar system, One (the Mercury) has zero moons, Four (Mars) has two moons, Seven (Uranus) has 27 moons

And

Three (Earth) has one moon

Hint:

Son is a synonym of Sun

• @DEEM edited thanks! nice riddle +1, but maybe the science and pattern tag instead of riddle? Jul 22 '19 at 12:06