Over those distances, even a sharp laser beam would spread to thousands of kilometres wide by the time it reached Earth.

Light sent into the oil layer was confined there, bouncing between the metal and air boundaries. The beam spread out ever more quickly, generating a trumpet-shaped glow (see image).

Powder can be spread onto a tray and then solidified in the required pattern with a squirt of a liquid binder or by sintering it with a laser or an electron beam.