Lumenna-Súnáris System (5): Eliéra

I/4. Eliéra

Class: Sylithotectonic (simulated)
Orbit (period): 0.993 au (361.1075 T-days; 333.33 local days)
Orbit (ecc.): 0.023
Radius: 5,000 miles – special
Mass: 5.614 x 10²⁴ kg
Density: 6.2 g/cm³
Surface gravity: 0.94 g

Axial tilt: n/a
Rotation period: 26 T-hours

Black-body temperature: 265 K
Surface temperature (avg.): 284 K

Atmosphere: Standard atmosphere.
Atmospheric pressure (sfc.): 0.94 atm
Hydrographic coverage: 60%

Satellites: 1 major (Seléne); 1 moonlet (Elárion).

Ah, yes, Eliéra. Homeworld of the eldrae. The jewel at the center of the Empire, and therefore the universe. The shining center from which the light of Order, Progress, and Liberty beams out into the galaxy.

And, curiously enough, not actually a planet at all.

It’s a Precursor-built Big Dumb Object. (Well, okay, technically it’s actually a Big Terrifyingly Smart Object, but that’s the accepted term/acronym…

…yeah, you know what? From now on, hereabouts, I’m redefining BDO to mean Big Damn Object, which strikes me as much more in the spirit of the thing.)

But anyway: it’s not a planet. It’s a flat disk – well, okay, not quite. It is almost a flat disk, with smoothly curved edges because while it’s 10,000 miles in diameter, it’s only 200 miles in height. Those smoothly curved edges mean that you can, in fact, sail right around the edge of the world to the other side and never bump into an actual “edge”; or at least you could were there not a giant perpetual storm where the two sides’ weather systems slam into each other in the way. It’s also almost flat because the builders wanted it to look flat, meaning that it’s actual gross shape is slightly convex, such that it looks flat after the refractive index of the atmosphere is taken into account. It spins like a flipped coin along a spin axis tangential to its orbit, which provides it with a day-night cycle.

At this point, several questions ought to be leaping to mind:

1. How does it keep its shape?; and
2. Those figures for volume/mass/density don’t look right.

I mean, Eliéra, as you would expect from its gravity, masses about 0.94 what Earth does. Its crustal density is a little heavier than Earth’s density, but not by much. (6.2 g/cm³). And yet its volume, being a disk 10,000 miles across by 200 thick, is only about 1/17^th of the Earth’s.

You should definitely, at this point, be wondering how the hell that adds up.

Well, that would be the lump of Mystery Matter™ down at the core layer that lets it hold shape under its own weight, and which is also responsible, it is believed, for the physics-defying weird-assitude of its gravity field.

(Said weird-assitude, as brought up here as the divide between Terrestrial and Celestial Gravitation that had entire generations of physicists and astronomers beating their heads on things and complaining about how much they hate special cases, is that said Mystery Matter™ does not obey the inverse-square law. Gravitational attraction to it is governed, instead, by the Because We Are World-Constructing Sufficiently Advanced Precursors And We Bloody Well Say So Law.

The practical result of this is that if you are in low Eliéra orbit, say a 10,100 mile orbit (i.e., 100 miles above datum), your stable orbit will skim the atmosphere in what is basically a disk shape orbit matching the gross shape of the “planet”. If you are in high Eliéra orbit, contrariwise, say a 100,000 mile orbit, your stable orbit will be a perfect near-circular ellipse, just as it would be around a perfectly normal planet, and your altitude above datum will vary accordingly. Stable orbits in between occupy shapes in between, exactly as if there was some meta-law changing the BWAWCSAPAWBWSS Law smoothly and continuously into the inverse-square law depending on how far away from the Mystery Matter™ you happen to be.

The consensus on this is that it is (a) space magic, and (b) fucking weird.)

3. How the hell does the geology/ecology work?

Mechan Ically.

Well, okay, not entirely. The Precursors who built it were very clever geotects and ecotects who arranged for as much to happen in a perfectly natural way as they could, but that couldn’t apply to everything. It’s very hard to have planet-like geological processes without a mantle and molten core, for example.

So, instead, they buried down in the big sealed core layer (that contains the Mystery Matter™) a giant massively-parallel array of nanocomputers – this being why it’s a Very Smart Object Indeed – complete with a whole ecological maintenance team in the form of “mechal elementals”, what its first civilizations assumed were nature spirits of one kind or another, that do the work of filling in the essential missing bits.

Which is to say: it’s a giant machine that worlds just as as hard as it can.

4. Does it have seasons? How does it have seasons?

Because binary system.

For half the year Eliéra is between its suns, and night is – instead – a faintly red-tinted as-bright-as-the-full-moon twilight, and both sides of the disk receive insolation at once. For the other half of the year, it’s opposite to the second sun, and its primary washes out its secondary’s contribution during the day while nights are actually dark, peaking at midwinter when Lumenna actually occults Súnáris.

The actual difference in solar input is very small indeed, but when chaotically amplified through feedback loops in the “planetary” atmohydrosphere, that’s how it has seasons.

5. Something else?

Of course, while I’m trying to answer the common but-hows, I’m too close to this to really have a good grasp on what they might be, so if you have more, please feel free to ask in a comment.

Moons

As for its satellites, it has two, both far enough out to be in comfortably conventional orbits.

I/4/a. Seléne

Class: Selénian
Orbit (period): ~325,000 miles (15.77 T-days)
Orbit (ecc.): 0.01
Radius: 1281.2 miles
Mass: 1.35 x 10²³ kg
Density: 3.30 g/cm³
Surface gravity: 0.20 g

Axial tilt: 4.77°
Rotation period: 15.77 T-days

Black-body temperature: 265 K
Surface temperature (avg.): 246 K

Atmosphere: None.
Hydrographic coverage: 0%.

Seléne is Eliéra’s major moon; it is very much like our moon, except for being somewhat more distant, and somewhat fatter, although curiously enough the apparent size from the surface is fairly similar.

Relatively low metal, silicate-rich, lots of fun stuff in its regolith, first to be colonized, you know the drill here. In later years it comes with helium-3 mining briefly, autofacs, cities, resorts, far-side observatories, and many millions of embodied sophonts living up there.

I/4/b. Elárion

Class: Gelidaceous
Orbit (period): ~1270000 miles (170.79 T-days)
Orbit (ecc.): 0.31
Orbit (inc.): 136.2°
Radius: 238.6 miles
Mass: 5.052 x 10²⁰ kg
Density: 2.14 g/cm³
Surface gravity: 0.012 g

Axial tilt: 51.4°
Rotation period: 0.46 T-days

Black-body temperature: 265 K
Surface temperature (avg.): 246 K

Atmosphere: None.
Hydrographic coverage: 0%.

Did I say conventional orbits?

Elárion is Eliéra’s weird-assed moonlet. An obvious extrasystemic capture (just look at that strangely-inclined, retrograde orbit), it’s a little (asteroid-classed, by the book; just smaller than Ceres) gobbet of ices and tarry organics that somehow wound up as a far and a distant moon.

From space, the surface seems oddly pink-red, due to said tarry organics. From Eliéra’s surface, of course, it’s barely visible, but those with good eyes looking hard enough in the right place can make out a tiny, tiny red dot in the sky.