NOVA bomb

Formerly mentioned in the popular well-selling novel, Halo: First Strike, the NOVA is hypothetically some of the most powerfull and some of the deadliest nuclear assosciated bombs to have ever been created by the UNSC.This particular bomb prototype had at least nine conjecturely high energied fusion warheads organized in the distinguishable pattern of a ring with each also containing an also conjecturly high powered lithium-triteride fusion core.Within it's rather unique yet precise course and process of detonation each of the nine lithium-triteride cores accumulate together consequenting in an unimbigulously monsterous blast that had been multiplied by approximately a hundred-fold. Holding up to there earned reputatable name "Planet-Killers", this particular bomb, consequenting from it's shear nuclear energetic blast of heat and radiation, was capable of destroying the majority,if not the entire, planet.

In the novel, they were left behind on the once valiant and celebrated Reach where they were "repurposed" by Admiral Whitcomb. His particular intentions were revealed in this noticeable quote "Either the Covenant pack those bombs up and take them home for study, a possibility that I hope to God happens. A bomb like that could crack their homeworld in two. Or, the bombs stay here, and they'll stop the Covenant on Reach..."

The resulting explosion detonated between the only known Covenant planet Joyous Exultation and its moon, Malhiem, scorching a quarter of the planet and shattering the moon, and the resulting winds on Joyous Exultation flattened cities and spawned tidal waves.

Delta Halo

In Ghosts of Onyx, Cortana requests that the UNSC launch a NOVA Bomb around Delta Halo and High Charity to stop the spread of the Flood and destroy the Covenant Holy Capital.

Trivia

The Nova Bomb was a bomb from the book Starship Troopers, wherein it is described as "being able to split a planet in half." It is likely that this had inspired the Nova Bomb within the Halo franchise.