SOLDIERis1337
The Immaculate
Incorrect. Crisis Core shows us that the environmental effects of the summons are nothing more than illusions, they show their opponent visuals that aren't really there. When Zack fought Ifrit it appeared as though he were in a magma filled hellhole, but in actuality he was still in the Wutai forest, no flames anywhere near him. Same goes for when you fight Bahamut in Banora and Bahamut Restu in Midgar. It appears as though Banora and Midgar were transformed into cloudy arenas, but in reality nothing had happened to them. Supernova is the same way. It shows an illusion to hit the player with a powerful magic attack.How can that be proved? Super Nova is a Summon. It's canon, just like Ifrit, Ramuh or KOTR. Ok, it doesn't kill anyone, but the HP damage can't be taken into account, it's a gameplay element, not a canon occurance. If the HP/MP system WAS canon, people who are knocked out wouldn't be in cutscenes. So, Super Nova did destroy at least the Solar System, and it did it canonically.
Even ignoring this devastating evidence, there is more proof that it didn't destroy any planets. We know from Crisis Core that Supernova was Sephiroth's signature move even before Nibelheim, he had used the move in his career as a SOLDIER, and the solar system is still very much intact. Then there's the fact that Sephiroth didn't want the planet destroyed, he needed it intact to absorb its lifestream. Sephiroth wouldn't use a move that would ruin his whole plan. Then there's the fact that if Sephiroth could call meteors before Nibelheim, he wouldn't have needed the black materia.
Supernova doesn't destroy any cosmic objects, it is nothing more than a powerful spell with an illusory sequence like many other summons.