Wrathful aliens are teaching the humans a lesson by relocating their world from a cosy 1 AU to around 4 AU away from the central Sun-like star. The planet is Mars-sized and covered in a salt-water ocean averaging at 6 km in depth with very little land. The atmosphere is Earth's in both composition and pressure at sea level, but the scale height is greater due to the lower, Mars-like gravity.
If no human intervention takes place, the oceans and atmosphere would condense and freeze, turning the world into something resembling Enceladus.
The humans hastily cobble together a plan: use a magical device capable of remotely spawning thermonuclear-like explosions at any location to constantly explode the depths of the ocean everywhere around the planet. The heat released into the oceans eventually finds its way to the atmosphere, warming it as well. (The magical device doesn't produce any nuclear fallout.)
Is this a viable method to save the planet (meaning, keep the oceans liquid and the air unsolidified)? If so: if the limit of explosive force delivered by the magical device is 10 megatons, and assuming we intelligently distribute the explosions to areas of ocean that need them most, how frequently do we need to detonate? Once a second? A hundred times a second? A thousand?