How to make a sphere from many small spheres

I'm trying to make this (picture found on internet):

So I added 2 spheres. One big and one small.For the big one I added : Particules > Emitter > Render > object > I selected the small sphere

And it gives me this :

Do you know why ?

(I tried to add "Rigid body" to the small sphere but it didn't change anything)

Thank you very much !