Event · M31

Battle of Pluto

The Battle of Pluto was an early major engagement of the Solar War, fought around 010.M31 at Pluto and its moons in the outer Sol System during the Horus Heresy. It set the Imperial Fists under Rogal Dorn against the Alpha Legion under Alpharius, whose true objective was the astropathic monitoring station on Pluto’s moon Hydra. Capture of that station would have blinded Terra’s outer surveillance while Alpha Legion sleeper cells and uprisings elsewhere in the system drew attention away from the attack. As part of Horus’s preparation for the drive on Terra, Alpharius set his fleet on a course for Sol under minimal power, the crews in stasis so that heat signatures would not betray them, and for about a year the ships drifted into the system undetected. Operative teams planted years earlier then struck across the Sol System: a freighter detonated over Terra, Damocles Starport was devastated, rebellion flared on Triton, and Headhunter cells under Kel Silonius activated Legionaries hidden in stasis on Terra itself, drawing Rogal Dorn and his Huscarls into a hunt that masked the real blow. Alpharius had switched identities with Silonius so that the primarch walked among the infiltration teams while the battle-barge Alpha and captains Ingo Pech and Mathias Herzog led the void assault. The Alpha Legion fleet of some two hundred warships struck Pluto and the moons Charon, Styx, Nix, Kerberos and Hydra. Imperial Fists forces under Sigismund, initially only about thirty ships, were badly outnumbered; fire ships and the captured fortress-moon Kerberos mauled the defenders. Alpharius led the ground assault on Hydra, releasing disabling gas across filtration stations, killing Captain Koro, and later finishing Centurion Gregorius Skekkir and the last Imperial Fists at the moon’s plasma reactor after the cruiser Spear of Verria had sacrificed itself to land reinforcements. Archamus, commander of Dorn’s Huscarls, discerned the true target and landed on Hydra, where Alpharius struck him down. At that moment the Phalanx arrived with a large reinforcing fleet of Imperial Fists and Imperial Armada vessels, having used the system’s competing gravity wells to accelerate their approach. Rogal Dorn teleported onto Hydra before Alpharius as Archamus lay dying. In the duel that followed Alpharius urged Dorn to join him for a different victory not fought for Horus; Dorn refused, tanked a spear-thrust in his shoulder to pin his brother—using a move he had once employed against a giant Ork—cut off Alpharius’s hands with the chainsword Storm’s Teeth, slashed him across the chest, drove the spear into him and finished by cutting through Alpharius’s skull. Kel Silonius ordered the Alpha Legion withdrawal, remarking that all in the Legion were one. Archamus died of his wounds. In the aftermath the Imperial Fists purged suspected Alpha Legion assets across the Sol System, while Omegon assumed Alpharius’s role within the Legion. The battle is distinct from the later, wider Solar War of 014.M31 that brought Horus’s main fleets into the inner system.

See where Battle of Pluto occurred on the galactic map during the Horus Heresy.

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