Create Level similar to Super Mario Galaxy

I want to create a level just like Super Mario Galaxy, where the character walks over planets (floating spherical levels) but never falls off from the corner. How do I do that? (Image attached)

As you can see here Mario is walking on top of this small planet but he is not falling, I want create something similar like this.

224849-gfs-68186-2-11.jpg

Sorted. Thanks sir :smiley:

google: ue4 mario galaxy gravity