From Halopedia, the Halo wiki
The planet has a green, icy surface. One of the most notable landmarks on the planet's surface is the Theran Crown, a gloomy, spire-studded cryovolcano ringed by green ice cliffs. Although Neos Atlantis features surface habitats, these are sealed from the exterior due to the planet's toxic atmosphere.
In March 2526, during the early stages of the Human-Covenant War, the 11th Marine Force Reconnaissance/ODST was stationed on Neos Atlantis, before moving to engage the emerging Covenant threat in the Outer Colonies. Lieutenant Commander Clovis Petriv of the Incident Response and Investigation branch and Captain Laru of UNSC Donoma had attended a senior leadership course on Neos Atlantis together.
On October 14, 2553, an Office of Naval Intelligence Ferret team consisting of Veta Lopis, Mark-G313, Olivia-G291, and Ash-G099 were conducting a training exercise in UNSC Recreational Facility 6055-NA-A situated in the Liberty District, which turned into a fight for their lives after they came under fire from multiple hostiles ostensibly under the direction of Dark Moon Enterprises.
Government and society
Neos Atlantis is a high-security world surrounded by orbital maintenance docks that only service United Nations Space Command military vessels. These installations employ close to 100,000 civilian technicians. The UNSC maintains recreational facilities on the planet which are reserved for the sole use of fleet personnel due to security concerns.
"Neos Atlantis" means "Young Atlantis" in Greek. The green-colored ice surrounding the Theran Crown could indicate the presence of some form of algae-like organisms, and thus life, on the planet. The discoloration could also be due to other impurities, such as sediments or air bubbles.
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