I'm developing a small space game, and this is how planets look

The planet meshes are dynamically generated using SurfaceTool. However, I want the edges between the triangles to not be so obvious. I would like the triangle edges to look smooth, like in a sphere mesh. I don't want to use a gazillion of triangles for that, because that damages the performance. Is there a way to do this? (this might fit in better in the shading forum)