How to make a 3d Spherical Planet with terrain and atmosphere

I’m making a new game in which you will be able to fly to, land on, and explore. My problem is I don’t know how to go about generating a Spherical Planet. Also, I when generating terrain, I would assume I could use Perlin Noise, but trying to implement this onto a sphere is where I am stuck. Also I wanted to know how to go about adding an atmosphere to each planet, so you will have a different sky, than in actual space. Any help or example code would be immensely appreciated!! I am also fairly new to scripting in Unity3d.

try a sphere with a bump map attached with a cloud layer that has some alpha(transparency values)

try putting a haylo to your planet and put the blue color on it