From Luce Gilmore, Cambridge, UK
In your report on the return of liquid mirror telescopes, you say that mercury would be too dense a material for building such an instrument on the moon(10 December 2022, p 41).
Why not use a sodium-potassium alloy, with a melting point of -4oC? These metals are cheap, very low density, won’t tarnish in a vacuum and reflect light better than mercury.
