Humans are trying to terraform Mars. The first step is to restart the magnetosphere. To do this, (and any naysayers who think that a magnetic dipole satellite is better can kindly not say so) a swarm of 100-metre parabolic mirrors are built in geosynchronous orbit around the planet. The mirrors are angled to focus sunlight into continuous, intense beams, which vaporise rock and create tunnels through the surface leading to Mars’ core. The beams gradually heat the frozen hearting of the planet, warming it until it melts. This produces a Dynamo that generates a magnetic field, not to mention several volcanoes from the tunnel shafts which will handily warm the planet up.
Assuming the mirrors are 99.6% reflective, (of visible light, at least) and that there are a thousand of these, evenly spaced in their orbits around the planet’s equator, how long would it take for them to tunnel their way to the core, and how long would it then take to melt it?