Another problem is that when you land onto the surface, you can see the edges of the faces on the planets, which indicate they're not quite round enough.
It shows that the planets have 32768 faces, each face takes up 1.4 degrees of their surface volume, so there are 256 segments and 128 rings (as based on Blender's view on UV Spheres).
The planets need to have at least 131072 faces (512x256 divisions), and then therefore the edges would be virtually indistinguishable, with 360x180 divisions (64800 faces), each face would take up only 1 degree of the surface volume, and you wouldn't notice the out of roundness, so the 512x256 resolution would be better than a 256x128 resolution.