Panthalassa

Panthalassa is an inhabited superterrestrial waterworld.

Etymology
Panthalassa shares its name with the only ocean that existed on Earth during the Permian. The name means "all ocean".

Physical characteristics
Panthalassa has a mass 3.85 times that of Earth (2.2993·1025 kg) and a radius of 10,265 km. Ignoring oblateness, those parameters give a density of 5.075 g·cm-3 and surface gravity of 14.6 m·s-2 (1.49 g). Panthalassa's density being 92% that of Earth is due to high quantity of water.

Structurally, Panthalassa consists of an inner silicate-iron core and mantle with a radius of 9,920 km. They are covered by a layer of water ice 270 km thick, which is in term covered by a liquid water ocean 75 km deep.

The hydrosphere has 352 times more water than that of Earth. With a mass of 4.93·1023 kg (6.7 times greater than the moon), 2.14% of Panthalassa's mass comes from water.

Panthalassa is relatively young world, with just 2.4 billion years.

Geography
With a global 75-kilometer-deep ocean with a frozen seabed, Panthalassa has no main geographical features.

From space, it is entirely blue, except for the equatorial region, completely covered by clouds. This implies that a greater deal of water evaporates in the equator, because the axial tilt makes temperature vary according to the altitude. Strangely though, Panthalassa lacks frozen poles.

Atmosphere
The original atmosphere consisted primarily of water vapor (H2O) and ammonia (NH3). Their accumulation was the result of past cometary impacts.

Biosphere
Panthalassa harbors a native biosphere. Life is (presumably) carbon-based, using water as primary solvent. By the time of arrival of the Quercus, monera and plant-life existed. The formation of a corrosive nitric acid atmosphere was in fact prevented by the emergence of primitive life in the photic zone of the ocean, suggesting that Panthalassan life contributes to the nitrogen cycle as life on Earth.