Ontaheter is an unusually large ice world, with a core of silicate rock and light metals, and a trace atmosphere of krypton and xenon. The crust is mainly composed of water ice. Ontaheter's ice sheets show obvious signs of large scale fracture and refreezing, centered on a massive crater near the south pole.
A recent extranet meme suggests that a Prothean ship crashed through the crust of the planet before the collapse of their empire, and might still be recovered from the planetary core. This is purportedly the source of the planet's unusually high mass. Careful mapping of the planet's gravity field by orbiting satellites have proved that the planetary core is entirely normal.
- Survey: UNC: Valuable Minerals: Rare Element ×1 (Samarium)