Sphere 2 was a Delphic Expanse sphere encountered in 2153 by Enterprise NX-01.
Sub-Commander T'Pol theorized the existence of this sphere, located not far from Tarquin's planet, and turned out to be correct. Its level of gravimetric energy was much higher than that of Sphere 1. Captain Archer and Commander Tucker took detailed measurements of this sphere in a trellium-lined shuttlepod, as Enterprise could not get close to it. These measurements allowed T'Pol to calculate that there must have been at least fifty spheres in the Delphic Expanse. (ENT: "Exile")