The GodEngine, known to the Native Martians as Ssor-arr duss Ssethissi and when translated, the Engine of Ssethis, was a super-weapon created by the Ice Warriors from remnants of Osiran technology left on Mars long ago. This device could destroy a star by making it go supernova.
The GodEngine required a planetary mass to brace it against the subspace fields it generated. It was only operational in the absence of a bipolar magnetic field. One Ice Warrior group offered the Daleks the use of the GodEngine in return for the conquest of Mars for themselves. This was why the Daleks intended to remove the Earth's magnetic core.
To activate the weapon, a key was required which was actually shaped into the Sword of Tuburr. It was noted by the Seventh Doctor that the destruction of the GodEngine would fill subspace with exotic particles that would ruin the icaron generator. (PROSE: GodEngine)