Letter: Just one planet will do for an alien megastructure

From Robin Pratt, Glasgow, UK

Craig Hutton writes that to build a Dyson sphere, a civilisation would have to raid a vast number of star systems for materials (Letters, 20 February).

However, according to my rudimentary maths, just one small planet may do the job. Mercury is almost entirely made of metal. If you flattened it into a sheet and then made it into a sphere around our sun at Mercury’s orbital distance, then the resulting foil would be around 85 times as thick as the foil in my kitchen.

I wonder what any civilisation would do with such a vast power source. If you tap a star’s entire output, it is enough to move whole planets. Two possibilities come to mind: a game of intergalactic snooker or… a death star.