Ray Tracing a Tiny Procedural Planet [pdf] (casual-effects.com)

Wow, this is amazing. Thank you!

It takes a lot of talent to explain something complex simply and intuitively.

Nice!

https://www.shadertoy.com/view/lt3XDM

In the same kind of ideas, there is also a mind blowing trick with "Kaleidoscopic Iterated Function Systems" which allows for a very compact code by folding space to create psychedelic fractals. https://www.shadertoy.com/view/tdcGDj (move mouse, and view associated video for more).

What a fantastic, straight forward and enjoyable read. Well done!

On page 60 "CONCEPT ART (FROM OTHERS)" there are some beautiful images this guy used as inspiration, but I can't find a link or reference to their origin.

Does anyone know where they come from?

Spore 2?