Coat the metal in an ablative shield made of Martian rock (handwaving over how this is done), fire it to earth using a mass-driver, guide it in with an on-board

Coat the metal in an ablative shield made of Martian rock (handwaving over how this is done), fire it to earth using a mass-driver, guide it in with an on-board chemical rocket engine, and drop it into the Pacific for recovery (more handwaving). Of course, this also has other uses [1]. [1] https://en.wikipedia.org/wiki/Kinetic_bombardment https://en.wikipedia.org/wiki/Kinetic_bombardment