The Borg Queen's sphere was a Borg sphere attached to a Borg cube that was used during their attempt to assimilate Earth in 2373.
After the attacking Borg cube was defeated during the Battle of Sector 001, this sphere left the cube before it was destroyed, and traveled back to the year 2063, in order to prevent the First Contact. It was destroyed by the USS Enterprise-E, which had followed the Borg through the temporal vortex, but not before bombing Bozeman, Montana, and beaming the Queen and a number of Borg drones to the Enterprise. (Star Trek: First Contact)
Debris in the Arctic in 2153
Ninety years later, the remains of the sphere were later found by the A-6 excavation team in the Arctic Circle, buried under snow and ice of a glacier. Two drones had survived the crash and were preserved in the ice. Upon regenerating, the drones assimilated the scientists and collected all remains of the sphere to include it to the assimilated transport Arctic One. This transport was later destroyed by Enterprise NX-01 but not before they sent a message to the Delta Quadrant that would lead to the initial conflict with the Borg in the 24th century. (ENT: "Regeneration")
