Suppose we lived on a planet with two class m stars, occasionally (1% of the time) between one and two astronomical units away, two class k stars occasionally between two and three astronomical units, two glass G stars occasionally between three and four astronomical units, etc. It would be too cold most of the time, but occasionally it would get hot enough to melt the rocks, for a few days. Primitive life forms could survive only far below the surface, but who can say what technologically advanced life forms might have? I believe that would be thousands of times our present stellar density, but I don't know how to calculate it. Also I don't know how we can avoid super nova and a very rare class O star passing less than one astronomical unit which would cause the ablation of several meters of planet surface per hour. Please embellish, refute, and/or comment. Neil