I would imagine a bunch of photon torpedos would devaste the planet; one ounce of antimatter blew out half the atmosphere on the planet the cloud critter was from in Obsession.
It did indeed. Powerful stuff that antimatter.
Yep. More powerful than 10,000 cobalt bombs. One ounce on one side of the planet, another ounce on the opposite side - badda-bing, badda-boom. Done and done.
Too bad the landing party just didn't all have subcutaneous transponders on them. If that had been the case, Scotty could have just beamed everyone up and left. After all, the Eminians didn't have the means to force anyone to beam to the surface and Scotty wasn't going to beam anyone down, especially after the faked message from Kirk was shown to be such. And the Enterprise was able to avoid damage from the planetary disruptor banks so all Anan-7 would have been able to do was protest. After that, Fox could have negotiated some kind of a cease-fire from the ship or the Enterprise could have just left the system with critical information on the system.