Lumenna-Súnáris System (8): Melíeré

I/7. Melíeré

Class: Melíeréan
Orbit (period): 7.24 au (7,116 T-days/19.5 T-years)
Orbit (ecc.): 0.12
Radius: 38,372 miles
Mass: 9.81 x 10²⁷ kg
Density: 3.08 g/cm³
Cloud-top gravity: 5.43 g

Axial tilt: 22°
Rotation period: 14.0 T-hours

Black-body temperature: 98 K

Satellites: 9 close moonlets, ring. 3 major moons. 2 eccentric moons.

Melíeré is exactly what it looks like: like its closest counterpart, Jupiter, it’s a hydrogen-helium mesogiant with the traditional turbulent gaseous envelope around a whole bunch of metallic liquid hydrogen around a core. It’s a big, brawling, orange-red, yellow-streaked behemoth of a planet that successfully dominates the gateway to the outer system. Unlike Jupiter, it doesn’t have a single, distinguishing “Great Red Spot”, but it is known for enormous storm cells, the linaurrauken, which come and go upon its surface like pale blotches.

In the future, it becomes very significant in the outer system, first as a gravity assist, but also due to the plentiful energy resources available in the system and its relative proximity, in gravity well terms, to the e’Luminiarien Belt. It also acquires the families of gas mining stations common to major gas giants in the Empire and the Empire Nucleonics station for bulk-producing metastable metallic hydrogen.

It has a ring – not a spectacular Saturnine ring, but one which you can see from anywhere in the system, and a family of moons, of which three are major (I’m going to skip lightly over the moonlets and sub-moonlets at this time) and could be considered the equivalent of the Galilean moons: Kerasta, Isimír, and Cysperia:

I/7/a. Kerasta

Class: Thiorastan
Orbit (period): 383,389 miles (0.489 T-days)
Orbit (ecc.): 0.02
Radius: 522.7 miles
Mass: 8.809 x 10²¹ kg
Density: 3.53 g/cm³
Surface gravity: 0.085 g

Axial tilt: 1.40°
Rotation period: 0.495 T-days (tide-locked)

Black-body temperature: 98 K
Surface temperature (avg.): 75 K

Atmosphere: None.
Hydrographic coverage: 0% (unless you count short-lived sulphur pools)

Kerasta is very like Sol System’s Io: a seething, wracked sulphurous hellscape of tidally heated tectonic and volcanic fury. Expect sulphur geysers, molten rock, and general no fun on the surface here, and needless to say, the given surface temperature is for the parts that aren’t currently buried in the middle of the latest eruption. And then there’s the radiation, because just like Io, it has a flux tube.

Popular future activities in the region of Kerasta include some minor resource harvesting, tapping power for local activities out of the Kerastan flux tube, burying things that you’re very unlikely to want to see again, and types of extreme sports that would be considered pathologically idiotic for anyone who didn’t have a backup.

I/7/b. Isimír

Class: Inachian
Orbit (period): 613,423 miles (0.990 T-days)
Orbit (ecc.): 0.01
Radius: 716.5 miles
Mass: 1.525 x 10²² kg
Density: 2.37 g/cm³
Surface gravity: 0.078 g

Axial tilt: 0.29°
Rotation period: 0.990 T-days (tide-locked)

Black-body temperature: 98 K
Surface temperature (avg.): 84 K

Atmosphere: None.
Hydrographic coverage: 0% (externally)

Isimír’s surface is generally hostile, since Isimír has no magnetosphere worth speaking of, and as such its surface is routinely bombarded with horrendous amounts of radiation. It’s also not terribly interesting, being – in its essentials – one very large sheet of ice with occasional cryovolcanism when the crust is cracked by tidal forces.

The ocean beneath the ice, though…

Isimír has a lot of tidal activity keeping it warm, an order of magnitude more than even Kerasta. Between that and warm hydrothermal upwellings from its core, the Nighted Ocean of Isimír has long since given rise to its own autochthonous life, tiny plankton- and coral-analogues that thrive in the icy darkness.

In the future, there’ll be great colony cities here at the bottom of shafts through the crust, clinging to the bottom of the icy crust, and an ecosystem which is not, technically, the result of an ecopoesis project – it’s the result of artistic assistance to evolution, introducing new lifeforms designed based on the biochemistry and potential of Isimír’s native life.

I/7/c. Cysperia

Class: Cysperian
Orbit (period): 920,134 miles (1.819 T-days)
Orbit (ecc.): 0.01
Radius: 1,391 miles
Mass: 1.250 x 10²³ kg
Density: 2.65 g/cm³
Surface gravity: 0.169 g

Axial tilt: 1.12°
Rotation period: 1.819 T-days (tide-locked)

Black-body temperature: 98 K
Surface temperature (avg.): 103 K

Atmosphere: Thin nitrogen-methane atmosphere.
Atmospheric pressure (sfc.): 0.21 atm
Hydrographic coverage: 30% (thin hydrocarbon lakes)

Cysperia is the outermost of the major moons, with a small iron core – enough to give it a mild magnetic field and some protection from the radiation environment – and a mantle of mixed rock, ice, and silicate clays above its own briny ocean (this one, alas, lifeless).

Slightly more hospitable than its inner neighbors, Cysperia is both the future focus of most colonization efforts in the Melíeré sub-system, in partially-buried dome cities to shield from the radiation, and the gravity anchor for the majority of its habitats, other than those built into the lesser moons.