Experiment creating sphere impostors out of particles, rendered with MeshStandardMaterial.
The big sphere in the center is an actual sphere geometry. The rest are billboarded triangles.
I got the lighting right, but I couldn't get the shadows to work properly. This needs more time to investigate!
More details...
Credits
Based on Matt DesLauriers's Custom mesh standard material.
Coded using WebGL with three.js, isMobile.js and EquirectangularToCubemap