A smaller Borg vessel that travelled back in time after the Battle of Sector 001.
The Borg Sphere is a smaller, round vessel used by the Borg Collective for scouting and for independent missions away from the main fleet. Like the larger Cube it is a cold, dark vessel of exposed conduits, designed for function over comfort, and it houses drones who work in unison under the direction of the Collective.
The best known sphere emerged from the destruction of a Cube over Earth in the twenty-fourth century. Rather than retreat, it opened a temporal vortex and travelled back to the year 2063, hoping to prevent humanity from ever making first contact with another species. The USS Enterprise-E followed it through the vortex and found the sphere attacking Earth, where its weapons targeted the missile silo in Montana from which Zefram Cochrane was preparing his first warp flight.
The Enterprise crew, under Captain Picard, drove off the sphere and saved Cochrane's ship, the Phoenix. Before it was destroyed the sphere's drones had boarded the Enterprise, spreading across several decks and assimilating crew members, including an effort to take control of the ship's systems. The sphere itself was destroyed in the fighting above Earth, and history was left intact.