Hey Obama, whatcha gonna do now? I say nuke em. If the Norks want to play with fire, teach them and every other two bit dictator what will happen. The threat of this worked for decades during the cold war, and nuclear devastation of the North will send a clear and unmistakable message to Iran, China, Venezuela, etc., not to mess with a peaceful neighbor who is allied to the United States.
Update: The Japanese call for an immediate military response, and an immediate meeting of the UN security council.