NOVA bomb

"This is the prototype NOVA bomb, nine fusion warheads encased in lithium triteride armor. When detonated, it compresses its fissionable material to neutron-star density, boosting the thermonuclear yield a hundredfold. I am Vice Admiral Danforth Whitcomb, temporarily in command of the UNSC military base Reach. To the Covenant uglies that might be listening, you have a few seconds to pray to your damned heathen gods. You all have a nice day in hell..."

- Vice Admiral Danforth Whitcomb's recording on the NOVA bomb, right before it is activated in the space adjacent to the planet Joyous Exultation.

The NOVA bomb is a nuclear explosive device used by the United Nations Space Command. It contains a very high-yield combination of nine nuclear fusion warheads, which can create a blast capable of breaking a small planet into pieces. It is quite possibly the most destructive weapon utilized by either side in the Human-Covenant War.

Background
The NOVA bomb is a cluster of nine nuclear fusion warheads encased in a lithium triteride case. When the warheads are activated, the lithium triteride shell focuses the blast in upon itself, multiplying the destructive power by a hundred times. This gives the NOVA bomb an unprecedented payload for its size; the bombs are considered "planet killers" due to their destructive potential.

The NOVA bomb has been used in two known engagements: in orbit over the planet Joyous Exultation, and on the surface of the planet Glyke. In both cases, the effects were extreme. When the bomb was detonated above Joyous Exultation, it heated the planet's atmosphere, scorched one quarter of its surface and shattered a nearby moon. When detonated directly on a planet's surface—as was the case on Glyke—the explosion's power was enough to disrupt the planet's structure and overcome the binding energy of its gravity, turning it into a vast cloud of debris and killing every living thing in, on, and around the planet almost instantly.

Any further detailed analysis on the full power of this bomb has yet to be mentioned, but it is known that it is the most destructive weapon in the UNSC's arsenal.

History
It was intended for the NOVA bomb to be used in space against the Covenant fleet during the Fall of Reach. The remaining NOVA bombs were left on Reach and "re-purposed" by Admiral Whitcomb. His reasoning was that "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 first documented triggering of a NOVA bomb occurred when it was accidentally detonated by a group of Huragok stationed on the Covenant supercarrier Sublime Transcendence. Immediately after Kwassass, a fellow crew member, deciphered Admiral Whitcomb's message, the Huragok, through their curiosity and frenzied obsession, fixed the circuitry of the bomb, detonating it despite Kwassass's attempts to stop them. The Huragok completed the detonation timer's circuit, which promptly resulted in its activation. The resulting explosion occurred between a Covenant outpost planet Joyous Exultation and its moon, Malhiem, scorching half of the planet and shattering the moon. The resulting winds on Joyous Exultation flattened cities and spawned tidal waves. Radiation flooded the planet and killed everything living on it, penetrating the surface of the planet to its core. Every ship within the NOVA bomb's range, save for those on the opposite side of the planet, boiled and vaporized in an instant. The explosion was described as though "a small star had erupted between Joyous Exultation and its moon."

The NOVA bomb explosion completely destroyed three-fifths of the fleet that was there, totaling over 300 ships. Eighteen destroyers, two cruisers, one carrier and the flagship Incorruptible escaped the NOVA bomb explosion due to a Slipspace jump en masse just moments prior to the explosion. Other ships arrived to reinforce the Incorruptible arrived from Joyous Exultation, suggesting that they escaped the bomb's detonation as a result of being positioned on the opposite side of the planet.

During the Battle for Earth, ONI initiated Operation: SUNSPEAR and forwarded a high priority message to the Spartans of Gray Team, declaring "Condition: Endgame" under which they were to execute the detonation of a NOVA bomb on the surface of the Covenant colony world of Glyke, a major military production center home to billions of Sangheili. Deploying from the, Gray Team made landfall and activated the warhead on the planet's surface. Once out of range the NOVA bomb was detonated, destroying the planet and all life on its surface. Gray Team was unaware that the war was over and a tentative peace had been reached with the Swords of Sanghelios, making the action no longer necessary. During the Carrow Conflict in 2558, Gray Team were left worried about being charged as war criminals for their actions, but ONI offered them a deal which included a pardon by Thel 'Vadam for Glyke's destruction.

During the Battle of Installation 05, and the subsequent quarantine of the Installation and High Charity, Cortana requested that UNSC HIGHCOM deploy a NOVA bomb around Installation 05, to stop the outbreak of the Flood, and High Charity, in order to destroy the Covenant holy capital. However, it is apparent that this request was not granted, as High Charity was not bombed and later landed on Installation 00.

Trivia

 * The NOVA bomb shares its name with a weapon mentioned in the novel Starship Troopers, wherein it is described as "being able to split a planet in half." It is likely that this inspired the Halo universe's own NOVA bomb. A superweapon by the name of "Nova bomb" was also featured in the science fiction series Gene Roddenberry's Andromeda. The 'Nova Bomb' is also the name of a super ability in Bungie's Destiny franchise, that has the player launch a powerful explosive projectile at enemies.
 * In Halo: First Strike, Vice Admiral Danforth Whitcomb stated that the NOVA bomb on Reach had been activated on a timer. Though not stated, the bomb appears to have been disarmed at some point after its discovery, preventing it from going off until it was inadvertently reactivated during Halo: Ghosts of Onyx.

List of appearances

 * Halo: First Strike
 * Halo: Ghosts of Onyx
 * Halo: Envoy