Wee Planets, Tiny Planets or the Polar Panorama effect, whatever name you prefer, is the technique of taking a 360° panorama image and using Photoshop (or any other decent image editor) and creating a circular or round image that wrap the panorama around to make it appear like a tiny/wee planet.
Tiny/Wee Planet Tutorials
How to Create Your Own Planets Using Your Panoramas »
How to make Polar Panorama with Photoshop »
Producing Polar Panoramas »
Planetize your world [without photoshop] »
Tiny Planets Tutorial on Deviantart »