Create a material with faded transparent edges and an opaque centre?

I’ve been trying to create this material for a sphere using Fresnel. But, I’m unsure how to create the effect of an opaque centre, which gradually fades to transparent around the edges. So far all I’ve managed to do is create a sphere that is all transparent with faded edges. Is it possible?

Thanks!

Fresnel is clamped between 0 and 1. 1-Fresnel will make it more opaque at the center.