Planets: Altitude maps
It would be nice if the planets had altitude maps, so you could fly through the Valles Marineris on Mars, or the Grand Canyon on Earth. See #fan-creations for a proof of concept for Mars. The maps used are https://imgur.com/HIQ7R for the altitude map, and https://www.solarsystemscope.com/textures/ for the Mars texture. The latter has textures for the other planets as well, including the hexagon on Saturn, and the atmosphere for Venus.