If we had some convenient test planets handy I would bet against you when it came to optimal planetary suicide methods.
Orion's is a great idea for a different task but just not the solution to this problem.
/shrug
I'm the one who has read in detail about basic equational descriptions of nukes by their tonnage, targeting concerns, the engineering involved in going to megatonnage or gigatonnage range, etc. (I wanted to make a nuke simulation game), so you'll pardon me if I put more weight on my opinion than yours.
http://neo.jpl.nasa.gov/risk/2012da14.html
http://rt.com/news/paint-asteroid-earth-nasa-767/
Seems like a good opportunity to bring up existential risks. And A friendly reminder that NASA is in fact pretty damned important.
Thoughts?