I love this concept, did you knew it exists? Several panoramic pictures are add together and distorted to form a circle. This is simply done on photoshop ... And to do that, here's a very well done tutorial to help you make your first little planet. I love the work of Gavin Hoey and I advise you to subscribe to his channel on youtube. This really worths it!
And now brace yourself !!!! Yeah, because here are top flight of little planet:
This work is made by Catherine Nelson. Have a look to her other creations on her site here.