From Halopedia, the Halo wiki
Molaetra was a Forerunner-controlled planet in a triple star system within the Orion complex and the homeworld of Bornstellar Makes Eternal Lasting. Owned by Bornstellar's wealthy Builder family, it was shared by various lower-ranking Builder clans who also helped maintain the planet. Due to the stellar radiation from the three stars, the planet was protected by planetary shields; these caused noticeable refraction as the suns set beyond the horizon, along with the planet's natural aurora phenomena.
The entire planet was almost completely covered in artificial construction. Among the most impressive were the "disk seas"; artificial oceans each a thousand kilometers in diameter and a kilometer deep, overlapping each other by several hundred meters in a belt constructed along the equator. Cascades and twisting funnels of water connected some of the oceans, and Lifeworkers would often come and use them to experiment with various exotic lifeforms. In the northern hemisphere, there was a longitudinal belt of arched rockways, hundreds of thousands of kilometers of maze-like red and yellow sandstone formations stretching from the equatorial oceans to a perfectly circular icy pole.
List of appearances