Planet Profile: Arethusa

“From orbit the Arethusan oceans are almost indistinguishable from the planets landmasses. This is not a geological factor but owes instead to the large concentrations of aquatic plant life present on the ocean surface.”Green planet arethusa

Name: Arethusa

Atmosphere: Nitrogen/Oxygen (can support human life)

Surface Area: 0.86 Earths

Gravity: 0.93 g

Satellites: Arethusa has one small asteroidal moon orbiting at a distance of 24,000 km. The tidal force exerted by this moon on the surface of Arethusa is negligible. Arethusa also has a number of thin planetary rings, comprised of microscopic particles and debris fragments measuring no more than 1m across

Surface Geography

The surface of Arethusa is covered mostly by shallow fresh-water oceans and seas, with three large landmasses and an abundance of small island continents. Despite being slightly warmer than Earth on average, the planet still has considerable polar regions, which are covered by seasonal sheet ice.

From orbit the Arethusan oceans are almost indistinguishable from the planets landmasses. This is not a geological factor but owes instead to the large concentrations of aquatic plant life present on the ocean surface.


Arethusa supports multiple ecosystems, including mangrove swamps and open prairie. The most notable, and most unique habitat is the ‘carpet’ – a thick layer of plant life, which covers large portions of the Arethusan seas.

Floating grassland carpetThe Arethusan ‘carpets’ are composed of multiple plant species, which float on the surface of the water, or are anchored to the ocean floor. Over time, the leaves and vines of these plants become compacted, forming a thick, matted material. This eventually decomposes, becoming the base-layer for species growing on top of the carpet. The carpets are, in of themselves, a complex multi-layered ecosystem, supporting numerous insect species and providing grazing for animals and fish alike.

The Arethusan carpets are so thick that it is actually possible to walk across their surface. They are also vast, covering thousands of square miles. Originally, the carpets covered around 85% of all Arethusan oceans and seas, but this number has decreased since human habitation on the planet began.

The unique carpet ecosystems are able to remain largely unbroken due to the minimal tidal effect of Arethusa’s tiny moon, the shallow depth of the seas, and the resulting calm waters.

Flora and Fauna

Arethusa is home to a plethora of plant and insect species, but has relatively few large animal species.

The largest and most prolific animal is the ‘bulk’ – a large grazing herbivore. Large land carnivores once preyed upon the slow-moving bulks (these were hunted to extinction by humans) and the bulks evolved a unique defence mechanism; a thick layer of blubber covers their backs, and can be removed without harming the animal. This allowed the carnivores to feed, and the bulks to survive.

Today, bulks are farmed by humans, who periodically remove square sections of their blubber to be taken as food. This gives the bulks a bizarre chequered appearance. Bulk meat is extremely tough and not particularly nutritious, but it has a high fat and water content.

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  • Sid Jain

    I like the idea of the carpet! What effect do shallow seas have on the climate of the planet?