Niflheim
A land of mist, ice, and eternal cold
A colossal moon orbits a gas giant exoplanet with a mass approximately 2.28 times that of Jupiter. This exomoon is enormous, with a diameter twice that of Ganymede in our solar system. It is a frigid world, entirely devoid of an atmosphere and perpetually frozen. This is not surprising, as the gas giant’s orbit is very far from its small and dim red dwarf star, taking 61 days to complete. The moon’s name pays homage to Nordic mythology, where Niflheim is one of the primordial realms, a land of mist, ice, and eternal cold.
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
|
0,26 (Me)
|
0,78 (Re)
|
2,91 (g/cm3)
|
0,40 (g)
|
|
Type
|
Mass
|
Radious
|
Light
|
Temp.
|
Year
|
|---|---|---|---|---|---|
|
M
|
0,346 (Ms)
|
0,372 (Rs)
|
1,30% (Ls)
|
3201 (K)
|
61,1 (days)
|
Surface conditions
The surface of Niflheim is a vast expanse of ice, reflecting the faint light from its distant red dwarf star. The moon’s icy crust is marked by craters, deep crevasses, and towering ice cliffs, sculpted by ancient geological processes.
During its formation, a significant amount of volatiles were incorporated, resulting in a 3,000 km deep ocean surrounding a rocky core, which gradually cooled over millions of years. As it cooled, the water began to freeze from the top down, forming a thick ice crust that isolated the ocean from the surface.
Additionally, the depth of the ocean was sufficient to form exotic types of ice due to the high pressure, such as ice IV, which grew from the bottom, further isolating the liquid ocean from the rocky core. The rich volatile content of this world means that the core is small, cold, and contains few iron, nickel, and radioactive elements.
Consequently, Niflheim is a dead world, lacking geological activity that could melt the ice, provide energy sources and minerals for potential lifeforms, or maintain an atmosphere. As a result, a thin layer of ocean exists within the crust, completely isolated by hundreds of kilometers of ice from the surface and thousands of kilometers of exotic ice from the rocky core. The absence of geological features such as hydrothermal vents and volcanoes renders this ocean completely sterile.
This fictional world could exist around Gliese 876 b, a gas giant exoplanet orbiting the red dwarf star Gliese 876. It was the first planet found orbiting a red dwarf, using the radial velocity method, discovered in 1998. Gliese 876 is a red dwarf star located about 15 light-years away from Earth in the constellation Aquarius. Also, this structure with a layer of exotics ice and oceans beneath the surface is suspected to exist in Ganymede, a moon around planet Jupiter in our solar System.
More information about Gliese 876 b: