Abyssal Realms
A frosty exterior hides a deep dark ecosystem
A Mars-sized exomoon orbits a massive gas giant around a K-type star. The exoplanet is located in a distant orbit, taking nearly six years to complete one revolution. At this distance, the exomoon receives minimal sunlight, resulting in a cold and frozen environment. Despite having a substantial atmosphere, the sky is typically clear of clouds.
The high pressure and low temperatures allow for the existence of lakes of liquid CO₂. The surface is characterized by several mountains rising from the icy crust. The terrain is irregular, reminiscent of Mars, with approximately half of the surface covered by oceans. These oceans have a rigid 15 km thick ice crust and a warm 5 km deep liquid layer beneath.
In some areas, the crust is fractured, allowing the ocean to erupt onto the surface, creating enormous geysers that freeze quickly. These geysers send plumes of vapor hundreds of meters into the air.
Planet summary
The following table summarizes the characteristics of this planet, comparing its mass, radius, and gravity with that of the Earth (Me, Re and g). A similar table can be found below, comparing the characteristics of the star’s mass, radius, and light with our Sun (Ms, Rs and Ls).
|
Type
|
Mass
|
Radious
|
Density
|
Gravity
|
|---|---|---|---|---|
|
Exomoon
|
0,12 (Me)
|
0,55 (Re)
|
4,10 (g/cm3)
|
0,41 (g)
|
|
Type
|
Mass
|
Radious
|
Light
|
Temp.
|
Year
|
|---|---|---|---|---|---|
|
K
|
0,84 (Ms)
|
0.80 (Rs)
|
34% (Ls)
|
4909(K)
|
2190(days)
|
The deep ocean
The moon moves in an eccentric orbit that keeps its interior warm through tidal effects, making it significantly more volcanic than Earth. The ocean floors are scattered with hundreds of thousands of volcanoes and hydrothermal vents. In these areas, seawater seeps into the crust through cracks and fissures, where it is heated by underlying magma, reaching temperatures of up to 400°C (752°F) and becoming more acidic.
This superheated water dissolves minerals and chemicals from the surrounding rocks, including sulfur, copper, zinc, gold, iron, and helium, then rises back to the seafloor, carrying these minerals and gases with it. When the mineral-rich water exits the vent and comes into contact with the cold ocean water, the dissolved minerals precipitate out, forming chimney-like structures known as “black smokers” or “white smokers,” depending on the minerals present.
The column of warm water rises dozens to hundreds of meters until it cools enough to stop and spread horizontally. This process can create layers where different gases and minerals are more abundant.
Hot vents ecosystems
Chemosynthetic bacteria and archaea form the base of the food web, these microorganisms use the chemical energy from hydrogen sulfide (H₂S) and other chemicals emitted by the vents to produce organic matter. These bacterias grow on the bottom forming a thick layer of microorganisms, and creatures similar to alien trilobites feed on this bacterial grass.
The smallest, dug on this bacterial matt or bacterial grass, helping to introduce minerals and H2S. The big trilobites use the metals dissolved in the water to create an iron exoskeleton that protects them from predators.
The most dangerous is a creature similar to huge marine scorpions. Other creatures that live in this environment are giant networks of tubular worms that pump water rich in mineral feeding bacterias in its inside, and bioluminescent jellyfishes able to move around the column of warm water to reach layers where different minerals or gasses are more abundant.
Cold seepages ecosystems
A second type of environment emerges when the vents become old and hydrothermal activity diminishes. This leads to the local extinction of the existing community.
However, layers of dead bacteria, which can be several meters thick, slowly decompose, producing methane and hydrocarbons that gradually filter to the surface. A new community arises, consisting of bacteria that feed on methane and decompose oil.
Creatures resembling deep-sea corals with a hairy appearance develop a network of roots that penetrate the sediment, extracting gases and minerals. In some areas, the decomposed organic matter forms a dense, oil-like substance that slowly filters through the sediment. Alien mussels dominate this environment.
This world could be an exomoon around HD 181433 d, a gas giant exoplanet located approximately 87 light-years away in the constellation Pavo. It orbits a K-type star, HD 181433, and has a minimum mass of 0.54 times that of Jupiter, taking 6 years to complete one orbit. It was discovered in 2008 using the radial velocity method. Also, this kind of environment is similar to a geologic era of the planet earth where a massive glaciation extends to the equator, known as the “Snowball Earth”. And can be the present at icy moons in our solar system like Europa and Enceladus.
More information about HD 181433 d: