Introduction
The Wandering Isles is a largely system-agnostic setting that reconstructs the “floating landmasses” trope.
The world of Wandering Isles is an ocean planet with gravity and atmosphere relatively similar to Earth’s. The sky is populated by large lighter-than-air islands, floating above the cloud layer; each island is a wood-like mass containing large voids filled with hydrogen gas, with a thin inhabitable layer of soil on top. The planet’s strong magnetic field and powerful ocean currents interact to create occasional jets that spray ocean water high above the clouds, providing nutrients and water to the floating islands.
Astronomical data
The setting’s main planet, Tide, is a rocky planet with a radius of approximately 10000 km (60% larger than Earth’s) and a mass of 2.6×10^25 kg (4.4 Earth masses). Its surface gravity is approximately 15 m/s² (50% higher than Earth), and the surface is covered in a saltwater ocean to a depth of several hundred kilometers.
Tide is in a 1:5 resonance with its larger moon, spinning around itself in 34.25 hours.
Tide has one large moon, as well as two smaller moons in a binary system.
The large moon, known as the Empress, is much like our Earth’s moon. Its radius is 2100 km (20% larger than Earth’s moon) and its mass is 1.3×10^23 kg. The Empress appears greyish-white and is tidally locked, orbiting at 29000 km (twice the Roche limit) with an orbital period of 6.85 hours.
The smaller moons, known as the Twins, are nearly the same size and mass. Their radii are 1100 km and 1000 km; their masses are 1.0×10^22 kg and 7.9×10^21 kg. They orbit each other at a mean radius of 7700 km with an orbital period of 34 hours. The system orbits Tide at a distance of 350000 km with an orbital period of 548 hours (16 Tide days).
Atmosphere
The atmosphere is composed of approximately 17% oxygen, 52% nitrogen, 30% carbon dioxide, and 1% various trace gases. Atmospheric pressure is 4 bar at Tide level, falling to around 2 bar at 4-5 km above Tide level, where most of the islands float.
Tides and ocean jets
Due to the Empress’ extremely close orbit and large mass, Tide has very strong tides. These tides cause powerful currents in Tide’s ocean, allowing it to act as a liquid dynamo which produces a strong planetary magnetic field (much like our Earth’s liquid-iron outer core). This magnetic field interacts with the ocean to produce occasional enormous jets that propel ocean water high into the atmosphere. These jets can reach volumes of up to 1000 km^3 and heights up to 15 km, and often bear up various ocean life.
Floating Islands
Tide’s atmosphere is home to a family of large plant-like organisms known as skytrees. These skytrees form communities that grow into the base of Tide’s floating islands. A community of skytrees is held aloft by an expansive modified root network, consisting of large cavities filled with hydrogen gas and enclosed by light, balsa-like wood. This base is known as a reef, and is typically 1 or 2 kilometers thick in adult specimens. A reef can reach horizontal extents up to several hundred kilometers, and is rarely smaller than 10 km across.
The reef is covered by soil and water with an average thickness of 1 or 2 meters, with leafy growths that resemble Earth’s trees rising up from the skytree reef through the soil. Smaller plants and grasses also grow in the soil, and various animals participate in the reeftop ecosystem. Tide’s oceanic jets provide a rich bounty of nutrients from the oceans below.
Intelligent inhabitants
Tide is inhabited by two human subspecies, dwelling on the ocean surface and on the skytrees. Due to the difficulty of travel between islands and the ocean surface, they have little contact with each other.
Most of the oceanfolk lead a harsh existence at the edge of annihilation, battered by powerful tides, storms, currents, and oceanic jets. They live mainly on broken pieces of fallen skytree reef, which make for large floating barges. A few spots on Tide are sheltered from the ocean’s rage, allowing a more comfortable existence. The known safe spots are both poles of the planet, as well as the eye of a large perpetual storm near the equator.
The skyfolk live on the sky reefs, above the clouds, where plentiful sunlight and oceanic jets make for bountiful harvests. The vast open spaces and strong winds allow for the development of light, one-man gliders, and the brightly shining stars at visible at nighttime are revered all over Tide.