One Million Planets

This post originally started off as an attempt to reorganize the notoriously byzantine and inconsistent NoLWoCS planetary classification system from one of my favorite science fiction universes, Orion's Arm. I gave up about a third of my way in; it just has too many bizarre, obtuse baked-in assumptions to be salvageable.

So instead I wrote a d10-based planet generator.

If you need to populate a planetary system fast, just roll up a few of these babies and put them in a sensible order from their primary. It's not a complete system, and doesn't generate particularly bizarre configurations (such as Curie's World), preferring instead to stick close to the most commonly known varieties of planets. Still, it does produce some pretty interesting planets with which you can populate the heavens.

All art in this post is by Adam Makarenko.

HOW TO USE THIS POST

This is a series of roll tables intended for relatively quickly generating a solar system or just randomly producing a single planet. You are, of course, free to ignore any result you don't like. Now that I put it out here, it's yours to use however you wish.

Using the tables is pretty simple:

1. Roll Basic Characteristics (class and orbital parameters).
2. Go to the Class tables of your planet and roll Subtype and Satellites.
3. If your planet has large moons, go to the Planetoid Class tables and roll Subtype for each.
4. If your planet is an Oasis or Superhabitable planet, go to the Oasis Planets table and roll Subtype.

Easy as that.

BASIC CHARACTERISTICS

Roll Class

• 1-2: Planetoid (dwarf planets and large moons)
• 3-4: Terrestrial (rocky planets)
• 5-6: Superterrestrial (super-Earths and ocean planets)
• 7-8: Neptunian (ice giants)
• 9-10: Jovian (gas giants)

Roll Orbit

• 1-5: Normal.
• 6: Skolian. Extreme axial tilt, at least 70 degrees. Rather than spinning like a top, the planet rolls on its side like a barrel.
• 7: Tidally locked. One side always facing its primary, the other always facing away. May be halfway a scorched desert, halfway an icy waste, or more turbulent and moderate if a thick atmosphere is present to disperse the heat. It might be unchanged, if it's far away enough or if its primary is cold to begin with.
• 8: Spin-orbit resonance. Rotates exactly x times for every y revolutions around its primary. (Example: Mercury is in a 3:2 spin-orbit resonance around the Sun - 3 rotations for every 2 revolutions.) The primary may occasionally appear to move backwards in its sky. 
• 9: Retrograde. Rotates in the opposite direction it orbits, or orbits in the opposite direction as other bodies in the same system. May have been captured into orbit from somewhere else.
• 10: Eccentric. Extremely oval orbit; shoots out far away from its primary on its apoapsis, or zips very close by it on its periapsis. Might have extreme temperature variations.

PLANETOID CLASS

Subtype

• 1-2: Barren. Sterile rock pockmarked by craters, little to no atmosphere. Water ice deposits in craters of eternal darkness.
• 3-4: Kuiperian. Icy surface dusted with reddish-brown tholins. Tenuous atmosphere of usually nitrogen, prone to freezing solid. May have a subsurface ocean.
• 5-6: Cryonic. Covered in a thick layer of ice (water, CO2, ammonia, methane etc.). May hide a subsurface ocean underneath (water, water-ammonia-mixture, ethyl-alcohol etc.). May not have an ocean: icy mantle surrounding a rocky core, an even mixture of ice and rock, etc.
• 7-8: Cryovolcanic. Cold and extremely tectonically active, wracked by constant earthquakes and cryovolcano eruptions. Covered in sulfur frost layered over water ice.
• 9: Chthonic. Extremely hot. Highly volcanic, covered in molten lava flows.
• 10: Oasis. Moderate-sized, complex atmosphere, extensive bodies of liquid across the surface. Can support complex, mature ecosystems. (Roll on Oasis table.)

Satellites

• 1-2: None.
• 3-4: 1d10 small irregular moons.
• 5-6: Huge tidally locked moon, binary planetoid system. (Roll on Planetoid table.)
• 7-8: Faint ring system.
• 9-10: Roll twice.

TERRESTRIAL CLASS

Subtype

• 1-2: Barren. Sterile rock pockmarked by craters, little to no atmosphere. Water ice deposits in craters of eternal darkness.
• 3-4: Cytherean. Extremely dense, hot atmosphere, highly acidic or alkaline. May or may not have surface liquid.
• 5-6: Martian. Dry, irradiated, usually cold desert. Sparse, unbreathable atmosphere. May have had large bodies of water once.
• 7: Chthonic. Extremely hot. Highly volcanic, covered in molten lava flows. Might be a young rocky planet, the core of a dead gas giant, or simply too close to its primary.
• 8: Cryonic. Covered in a thick layer of ice (water, CO2, ammonia, methane etc.). May hide a subsurface ocean underneath (water, water-ammonia-mixture, ethyl-alcohol etc.). May not have an ocean: icy mantle surrounding a rocky core, an even mixture of ice and rock, etc.
• 9: Cryovolcanic. Cold and extremely tectonically active, wracked by constant earthquakes and cryovolcano eruptions. Covered in sulfur frost layered over water ice.
• 10: Oasis. Moderate-sized, complex atmosphere, extensive bodies of liquid across the surface. Can support complex, mature ecosystems. (Roll on Oasis table.)

Satellites

• 1-2: None.
• 3-4: 1d5 small irregular moons.
• 5-6: One huge moon (roll on Planetoid table).
• 7-8: Rocky or icy ring system.
• 9-10: Roll twice.

SUPERTERRESTRIAL CLASS

Subtype

• 1-3: Pelagic. Covered entirely or almost entirely in oceans, up to 15-20 km deep. May support life, microbial or more complex.
• 4-6: Abyssal. 100% ocean cover, up to 50 km deep. Sea floor covered in a thick layer of high-pressure, crystalline ice-VII. Mineral-poor seas ill-suited to bearing life.
• 7-9: Mini-Neptune. Extremely deep oceans of supercritical water enveloped by a thick hydrogen-helium atmosphere. Transitory stage between ocean planet and ice giant. The largest type of super-Earth.
• 10: Superhabitable. Thick atmosphere, largely even mixture of small continents and shallow oceans. Even temperature. Extremely conducive to life, even more so than Terrestrial Oasis planets. Can support practically rainforest-level biodiversity on its entire surface. (Roll on Oasis table.)

Satellites (roll twice)

• 1-2: None.
• 3-4: A multitude small irregular moons.
• 5-6: 1d5 large moons (roll on the Planetoid table).
• 7-8: Rocky or icy ring system.
• 9-10: Roll thrice.

NEPTUNIAN CLASS

Subtype

• 1-6: Cryo-Neptune. Cold, lonely, azure or greenish planet located far beyond the snow line, with a hydrogen-helium atmosphere rich in volatile ices - ammonia, methane, and so forth. May cross into the Kuiper belt.
• 7-9: Hot Neptune. Hellishly hot atmosphere, may be in the process of evaporating away. Gas envelope contains exotic volatiles or refractory materials. Can be any number of colors due to its exotic chemistry; may also glow red from thermal radiation.
• 10: Helium planet. So close to its primary the hydrogen evaporated out of its atmosphere, leaving only an envelope of pure helium. White or light grey, and cataclysmically hot.

Satellites (roll twice)

• 1-2: A multitude of small irregular moons.
• 3-4: 1d5 large moons (roll on the Planetoid table).
• 5-6: Spectacular ring system.
• 7-8: 1 large Oasis moon (roll on the Oasis table).
• 9-10: Roll thrice.

JOVIAN CLASS

Subtype

• 1-2: Cryo-Jovian. The coldest type, brooding beyond the snow line. Ammonia clouds lend it a yellowish, orange or reddish color.
• 3-4: Hydro-Jovian. Warm, orbits in the habitable zone. Clouds of dazzling white water vapor.
• 5-6: Azuri-Jovian. Much too warm for clouds to form. Clear, blue, featureless orb.
• 7-8: Hot Jupiter. Cloud decks of alkali metals, such as sodium. Dark, grey, hellishly hot.
• 9-10: Ultra-hot Jupiter. The very hottest gas giants, closest to their stars. Clouds of pure iron and silicates. Hot enough to give off a dim red glow.

Satellites (roll twice)

• 1-2: A multitude of small irregular moons.
• 3-4: 1d5 large moons (roll on the Planetoid table).
• 5-6: Spectacular ring system.
• 7-8: 1 large Oasis moon (roll on the Oasis table).
• 9-10: Roll thrice.

OASIS PLANETS

Roll here if you got an Oasis or Superhabitable-type planet from either the Planetoid, Terrestrial or Superterrestrial table.

Subtype

• 1-4: Gaian. Silicate crust, oceans of water, oxygen-nitrogen atmosphere. Familiar to humans.
• 5-6: Methanogenic. Water-ice crust, oceans of liquid hydrocarbons, nitrogen atmosphere with a colorful organonitrogen haze.
• 7: Ammonian. Silicate crust, oceans of liquid ammonia with dissolved alkali metals. Cold, nitrogen-nitrous oxide atmosphere. 
• 8: Vitriolic. Silicate crust, oceans of pure sulfuric acid. Extremely hot oxygen-nitrogen-CO2-sulfuric acid atmosphere.
• 9: Halogenic. Silicate crust, oceans of water mixed with hydrochloric or hydrofluoric acid. Oxygen-nitrogen-chlorine/fluorine atmosphere. Acid rains.
• 10: Carbonian. Graphite crust, diamond mantle, oceans of tarry hydrocarbons, carbon monoxide or carbon dioxide atmosphere with choking carbon smog.