From Halopedia, the Halo wiki
Sedaaro was a planet within the Large Magellanic Cloud, or Path Kethona. Many Forerunners settled on this world following their massacre of the Precursors, weighed down by their guilt and as such refusing to return to the Milky Way. The inhabitants of this Sedaaro's ecosystem, all descendants of the Forerunners who settled the world, were most likely killed when the Master Builder Faber-of-Will-and-Might fired Omega Halo at Path Kethona at the end of the Forerunner-Flood war.
Located near the center of the Tarantula Nebula, Sedaaro orbited a small, orange star and was the innermost planet in its four-planet system. Like Sedaaro, two of the other worlds were small and rocky, and the last planet was large and very icy.
Prior to colonization, the planet was barren and uninhabitable. The planet's crust had a large amount of radioactive ore and its ocean was rich with deuterium. Oxygen, methane, sulfur, and chlorophyll compounds were detectable on the world. The planet's axis was perpendicular to its orbit. As such, the world never suffered with heavy winters or severe glaciations. The weather was consistent; it was typically cloudy on the world. There was infrequent but violent thunderstorms and heavy precipitation that would bring small amounts of snow to the planet's tallest mountains. The only ocean on the world was small and covered the southern polar region. Its waters were dense and salty, and filled with bitter minerals. All of water sources on the planet were contained in deep and clear freshwater lakes, some of which surrounded the planet's tallest, craggy mountain range. A thin lava dike had punctured one of the lakes and caused large amounts of flooding that shaped the terrain of the northern regions of a massive plain.
There was a kind of herbivorous Forerunner species on Sedaaro. These creatures were large animals that preferred squatting. Their faces still largely resembled those of Forerunners, with eyes closely spaced. Their digits and phalanges were still recognizably Forerunner. These animals were used as livestock by the sapient inhabitants of the world. Other animalistic types were also present on the planet.
There were several plants and mosses created from genetically-altered Forerunners. The plants would serve as a food source for the herbivorous creatures, which in turn supplied the sentient Forerunners with meat. Thus, the species were able to maintain a stable biosphere. The plants were scrubby and set low to resist the wind. Some were in the form of gray-green bushes and others had stalks topped by spiky leaves with wrinkly looking fruits or pods beneath. The moss and lichens were orange and fibrous. They could move on their own and scratch markings in rocks with their roots from memory.
Late in Forerunner-Precursor war, after the Forerunners had already eradicated the Precursor presence in the Milky Way and followed them to Path Kethona, the ancestors of the Forerunners invoked the Mantle and disobeyed their commanders' orders to complete their genocide of the Precursors. Some were summarily executed aboard their ships, while others were marooned on Sedaaro. A functioning biosphere was created for the barren world—either by the exiled Forerunners themselves or those who abandoned them—using Forerunner genetics to create a range of plant and animal species. As the Forerunners' genocide of the Precursors continued, two Precursors had found shelter and were found by the Forerunners who hid them and tried to heal them. However, the Precursors were beyond their ability to save and although the Precursors possessed the ability to heal, they chose to let nature take its course. Those abandoned on Sedaaro were the only Forerunners to survive the conflict, as their compatriots within the fleet ultimately refused to return to the ecumene as well, not wishing to spread the shame, fear, and knowledge of their actions. The two Precursors hidden on Sedaaro ultimately died. However, after dying, they became flora that was later studied and encoded, seeds that germinated for a million years. Sprouts that climbed to the surface took even longer and bloomed only in the last million years before the planet's rediscovery by the Forerunners.
Sedaaro and its inhabitants were rediscovered by the crew of the Audacity, led by the Librarian, circa 98,395 BCE. After landing on the planet and finding a village inhabited by these strange Forerunners, the Librarian was taken by to a canyon by the village elder where the ancient memories of the Forerunners that first arrived were stored. Here the Librarian spent several days interpreting the carvings created by mosses and the spores she inhaled. Driven by her own geas from the Precursors to fix the path and set right what the Forerunners did wrong, the Librarian located and collected the Precursor plant specimens. After this exploration, the crew of the Audacity departed Path Kethona, returning to the Milkly Way without reporting on the two Precursor specimens to the Ecumene Council.
During the final stages of the Battle of the greater Ark, Omega Halo was fired in an attempt to stop the advance of the Precursor star roads. While decimating a small portion of the star roads, the blast also purged the satellite galaxy of all sentient life, while the star roads ended up destroying Omega Halo and the greater Ark anyway. Thus it is highly probable that the Path Kethona Forerunners were annihilated by the Halo blast, and since it is not known if any of them were indexed or taken back with the Librarian, the subspecies has been rendered effectively extinct.
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