Libratia's Solar System
by Chris Wayan, 2011-12
for generations of shivering, patient astronomers
--solar system--tour the night--
More worlds? Planetocopia!
I've only roughed in Libratia's solar system, but it has six to ten sister planets (depending on how broadly you define "planet"); several have life of varying complexity and richness.
The inmost world, Hermes is less than a million km from the sun! It's a hot airless planet a little bigger than Luna. Yet it has a small sea: on the dayside near the noon point, where rocks with low melting points have pooled. Sure it's a sea! Surface liquid is surface liquid. Maybe there are silicon fish in that molten black sulfur. They've had long enough to evolve--that sea is no ephemeral thing like a Terran lava flow. It's been simmering there a billion years at least.
And the Black Sea's not the only hot spot: Hermes is a busy little planet with more volcanoes than Earth, if not as fierce as Io's. The reds and yellows you see are mostly sulfur compounds from them. Libratia has pulled Hermes into an eccentric orbit, so tidal stress heats the interior. Mountains rise around faultzones much like our rifts and subduction zones. Impact craters are quite rare.
Strangely enough, even the dark side shows visible traces of those volcanoes. They outgas water vapor, and what isn't lost to space freezes on the surface--unlike Mercury, Hermes is truly tidelocked, so its dark side is permanent--and cold. The ice is thin and patchy, but covers millions of square km, with holes around volcanoes where they've melted or vaporized it. A big white moth-eaten blanket.
Ha. Fire and ice! Hermes is closer to the classic tidelocked model than Libratia ever will be.
At its near approach, Hermes is visible even in Libratia's day sky--it's a bright crescent one-fifth the width of our moon, sometimes with a faint "old Hermes in the new Hermes' arms"--the bright ice of its nightside reflecting Libratia-light.
These sun-baked rocks are much smaller than our asteroids; dry, dense, and metal-rich. Lighter materials evaporated long ago. There aren't many, and they're in tight clusters; Libratia is large and close, so it acts as a harsh gravitational shepherd. Only a few sweet spots are stable.
With 1.4 Earth masses, Libratia is the big kid on the block; it may have stunted planetary formation in the inner system, as Jupiter probably did here.
These twin planetoids orbit each other just 20,000 km apart. Hazel's 2000 km across and Peanut 1500. Even lumped together, they're much lighter than Luna--no bigger than Pluto and Charon. Big enough rocks to be round, but my definition of 'planet' is something big enough to exhibit change; active tectonics, or an atmosphere or hydrosphere. (Yeah, my test makes Mercury doubtful--sue me).
Whether we call these twins planets, dwarfs, or big asteroids, their orbit is nearly as eccentric as Libratia's, and resonates with it; they orbit in two Libratian years (eight Earth days). Too bad they're so small, for they demonstrate another solution to the tidelocking problem; they ignore the sun to face each other. If they were a hundred times more massive, they'd be excellent candidates for life.
They do light Libratia's nightside: at their closest they're small silver disks, a tenth and a fifteenth the width of our moon.
CLAIREis as big as Mars. Poorer in iron, richer in water ice. Richer in air, too--0.3 atmospheres, a bit more than you'd find atop Everest. Unbreathable for Terran animals, though--mostly nitrogen, traces of CO2, and just 5% oxygen. Still, any free oxygen suggests extensive life. But where is it? Claire looks like a barren patchwork of Mars and Europa: feathery cirrus clouds float above rusty cracked ice-covered seas and brick-red, volcano-studded continents. A hot afternoon can briefly creep up past freezing, but not for long.
VITRIA, Claire's huge moon, orbits just 35,000 km out. Well, actually, Claire and Vitria orbit a common center of gravity between them, though much closer to Claire; it'd be fairer to call them twin planets, not planet and moon. How huge is huge? Vitria's bigger than Luna, nearly as big as Titan--well over half the diameter of Claire, and over one-fifth the mass! Big enough to hold onto a Martian atmosphere and have similar ice-covered seas--though the ice is much thicker. Vitria's cold.
Vitria and Claire are of course mutually tidelocked. Both have a day around half an Earth week long (exactly one-eighth the Clairean year). In deep time, this may change; as solar tides eventually slow Claire's spin, they'll also coax Vitria to spiral out as Luna did--the synchrony may break and the sun may even peel Vitria away. Olympia's a red dwarf, with 100 billion years to work on it. But for now--"now" as in the next few billion years--the tidal tug-of-war between Vitria and Olympia heats Claire's core so it's more tectonically active than Earth. This may be why Claire has a respectable atmosphere for a small world. That air has consequences: though cold, it's an insulator and greenhouser; Claire's sea-ice is in many places thin enough so light reaches the underside, allowing photosynthesis. So Claire's seas are more like Earth's polar ice than the dark Europan seas of Vitria, or Libratia's nightside. Large, complex sea life may thrive on Claire--coral reefs and kelp forests! It's the system's biggest fishbowl.
Claire and Vitria light Libratia's nightside even better than Hazel and Peanut: Claire's a rusty Mars with visible cloudpatterns, up to a fifth the width of our moon--the brightest thing in Libratia's night sky. Vitria's a similar little penny, but just one-eighth the Moon's width.
I can't honestly call it a gas giant at just 2.9 Earth masses, but in this little system we're already far enough out in the cold so a big protoplanet easily collects a lot of helium and hydrogen. Rocky planet? Gasbag? Neither, really--despite Bathos's rather Jovian appearance, it's a water world. That dense cloud-banded atmosphere rich in hydrogen, helium and ammonia hides deep worldwide oceans, down where atmospheric pressures are high enough to trap heat.
Bathos may well have life, down in those dark seas. But without a steady energy source like sunlight, complex life may be sparse or absent; like our abysses? Or will plants here be clever enough to harvest the fitful, actinic flashes from the constant lightning? Or the chemical energy from the compounds lightning creates as it burns through the dark? Don't hold your breath.
On second thought, do. Lightning in this atmospheric soup yields rich organics--but toxic. You'd be better off snorting glue. Let's move on; I don't like Bathos. All that sturm und drang thundering away! Too Gothic for my blood.
But it makes a wonderful nightlight. At its closest, 11 million km, Bathos is a golden paisley ball one-fourth the width of our moon; the largest of Libratia's nightlights, though Claire, being better lit, is a little brighter.
A low-density rock/ice world as big as Venus (90% Earth's diameter!) but just half Earth's mass and 5/8 Earth's gravity. It's like a much bigger Titan on a balmy interglacial day: warmer (130°K, -143°C, -225°F), hence 'wetter' (if you call gasoline wet). Air pressure at sea level is fully 4 atmospheres--mostly nitrogen hazy with hydrocarbons evaporating off wide (if shallow) ethane seas--not mere polar lakes, but 35% of the surface. Rain won't be a rarity, as on Titan. I'd bet on strange but complex life on both land and sea, though it'll be slower-growing than on Earth (the dim light limits available energy). That plus the cold may make for leisurely action, slowing down evolution; life may still be primitive. But Titania's got time. Its sun will be there essentially forever.
Sorry the illustration's so blurry; this is the best Libratian astronomers can do, given the hazy atmosphere and dim sunlight this far out.
From the nightside, Titania's a dull yellowish disk just a twelfth the width of the moon.
The outermost world locally known: a dwarf Neptune, just 3.2 Earth masses--but that makes it the largest known planet here! Yet from Libratia's nightside, it's just a dim green fuzzy spot, neither a point nor a disk. Twice the diameter of Earth and closer than Venus is to us, it'd look bigger than Titania, it were well-lit; about a tenth the width of the moon. But its dim rim fades into the outer dark.
Just like our solar-system tour. No clear end...
Another mini-Neptune at 5 Earth masses, but one so dim and slow it's simply hasn't been noticed from Libratia, though it's the biggest planet in their solar system! Does that seem unlikely? It happened here, with an even larger, brighter planet. Uranus is visible to the naked eye, yet not one of the thousands of human cultures staring at the night sky ever noticed it was a planet. You know, those things consulted astrologically, sacrificed to, worshiped as gods? Well, we carelessly overlooked a god!
So give them credit--at least the Libratians noticed Cronos. Though they didn't worship it--or any planet. Most of Libratia's habitable regions have short nights or mere dusks; and the air is dense. Only Hermes, Claire/Vitria and Bathos are dimly visible in the day-sky--most are drowned entirely. Whole regions are so cloudy you can rarely spot the sun. Planets? What are planets?
And the best seeing conditions are deep into the night side, past the border-storms. Slight supply problem there, of course. There's exactly one observatory there, in the South Rift. Three small scopes, hungry shivering observers, and a huge night sky... It's understandable they haven't noticed X--yet.
Here's an unlikely view from South Rift. The planets throw a party and invite a big loud stranger called Luna, for comparison. They set up a neat reception line in orbital order, to show you their size and brightness--or rather their smallness and dimness! These aren't the huge romantic moons of science fiction book covers, are they? But don't go dissing them for that. They aren't moons at all! Planets, remember? Those specks of light in Earth's sky, that never show a visible disk?
So give those bundled-up astronomers a few more centuries. X is big enough to spot, just so damn dim. Remember, it's further from the sun than... Mercury!
I did tell you this system was small.
Once a fur-bundled, shivering South Rift astronomer plots the orbits of the visible worlds, she won't just find the perturbations of X: even its invisible sisters are close enough for their gravitational influence to be quickly obvious. For unlike Uranus and Neptune, Y, Z (and On Beyond Zebra) won't have orbits lifetimes long; just a few Earth years. They orbit closer than Earth, after all! Olympia may be stingy about light, but its gravitational muscles aren't that weak; small or not, it's still a star.
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