Planet 4546B

Planet 4546B is a category-3 ocean planet on which the story of Subnautica and Subnautica: Below Zero take place.

The planet got set up as a research outpost by the Architects meant to study a bacterium called the Kharaa Bacterium. The Kharaa Bacterium is a highly infectious alien bacterium discovered by the Precursors during the exploration of another world and set up research outposts on planets to find a cure. 4546B is one of these outposts.

Overview
Planet 4546B is located in the outer reaches of the Ariadne Arm, orbiting around the star 4546. The “B” means that 4546B was the first planet discovered around the star 4546 (or 4546A). There are at least ten other celestial bodies in the system, each of which is larger than Earth's Moon. Planet 4546B itself is a water planet smaller than Earth with a breathable oxygen-nitrogen atmosphere. It also harbors two moons, one being very close to the planet, causing frequent solar eclipses.

There are three known major ecosystems on the planet: the Crater, Sector Zero, and the Dead Zone, the latter of which covers the majority of the planet.

The known planet is almost completely covered in water, except for a few islands, and features a variety of submerged biomes. The Aurora is located a few meters above the surface, in relatively shallow water.

The Crater features a full ecosystem of flora and fauna. However, this is only a very small area of the planet, located in a dormant volcanic crater, approximately 2km in diameter. The Arctic supports a nearly completely different ecosystem, harboring more creatures and plants adapted to the colder temperatures. The rest of the ocean is known as the Crater Edge, it is extremely deep and nearly devoid of life, supporting only microscopic life forms, and Leviathan Class Organisms. It is unknown whether any similar areas of life exist elsewhere other than the Crater and Sector Zero.

Architect and PDA data make note of high thermal activity from the planet's core. This is evidenced by the Inactive Lava Zone and Lava Lakes, respectively. The Architects took advantage of this feature, installing the Alien Thermal Plant within the Lava Castle, which allowed the generator to harness the planet's natural thermal energy.

A day and night cycle on Planet 4546B lasts about 20 minutes of real-time.

Story
Around 1000 years prior to the events of Subnautica, the Architects arrived at Planet 4546B, setting the planet up as a research outpost to find a cure for the Kharaa Bacterium.

Following Ryley Robinson's return to Alterra, the aforementioned company installs a number of bases and outposts throughout Sector Zero, and presumably the entire planet, to harness its natural resources and conduct research on the secrets the planet holds.

See Storyline for further information.

Trivia

 * Planet 4546B is most likely located in the Habitable Zone, a section in a planetary system where life can thrive, and water exists in liquid form.
 * However, given the size of the planet's parent star, 4546, seen during the loading screen, Planet 4546B can't be within the Habitable Zone. However, the in-game star appears to be closer than in the loading screen. This is most likely a developer oversight, or purely artistic representation.
 * Another likely explanation is that the star 4546 is actually behind the viewer's perspective, out of the image.
 * Planet 4546B may be based on the real-life planet Gliese 1214B, as both appear similar in appearance, and are both "water worlds".