Wow, what a tangent! But if clarification is needed in order to stop rampancy then allow me to offer the answer by the math.
Yes, to destroy a planet would require an absurd amount of energy, but it depends on your method of destruction. The Earth, for example, has a mass of around 5.97*10
24 kg. Antimatter, as mentioned in the earlier posts, has a 1:1 ratio of energy output, as in there is total conversion from mass to energy. Since E = MC
2, we can now plug in the mass of the earth to find how much energy the Earth is equal to. E
Earth = 5.97*10
24*299,792,458
2, so to completely convert 5970000000000000000000000 kg of matter into energy would take 5.3656e+41 joules, or 1.2824e+26 megatons of TNT. But that would be suggesting you are atomizing the Earth, and you would need enough antimatter to produce that much energy. THAT IS A LOT!!! But you could crack the Earth into asteroids with well-placed nuclear devices, or if we fancy being ever still fantastical, send a bunch of nukes to the center of the Earth. And by a bunch I mean more than what we have currently produced to date. But then we get into pressure and a totally different math, so let's leave it at that.
In either event, the original discussion was dealing with the destruction of Halo, which is 10,000 km in diameter, and but a scant mass in comparison to Earth. Also, the halo was a balanced system rotating and relying on the completed shape staying intact. The ring simply rotated to death once a small hole was blasted out of it by the cruiser self-destruct.
The NOVA bomb, the "planet-killer", was described as a cluster of nukes arranged in a lattice inside a trituim casing. The explosions worked as modern fusion warheads do; the smaller bombs compressed the more volatile materials together to create a split second of fusion. The book suggests a yield one hundred fold, which I can only assume is based on the modern, real-life calculation that a cluster of fission warheads around a fusionable material has, in reality, made a small fusion reaction that made the bomb around 100 times more powerful. Assuming the NOVA is such an arrangement, with fission nukes surrounding fusion nukes surrounding a solid fusionable material, then it isn't a far cry to imagine that it would be 100 times more than the individual bombs. So a bomb such as that would have dire effects if placed on a planet. It would shatter smaller planets, but for a planet the size of the Earth it would probably blow a nice chunk into space and basically cause the rest of the planet to roast or undergo some serious nuclear winter. In either event, it would render the planet uninhabitable.
So, whether it's vaporizing a planet or just making it a desolate, barren rock, remember this: it's sci-fi, where imagination runs wild and science becomes so advanced we can't predict what will be possible. As Arthur C. Clarke said, "Any sufficiently advanced technology is indistinguishable from magic. "
For further reading:
http://en.wikipedia.org/wiki/Clarke's_three_lawshttp://www.1728.com/einstein.htmhttp://www.stardestroyer.net/Empire/Tech/Beam/DeathStar.htmlhttp://en.wikipedia.org/wiki/Planet_killer
