Science // Gas giants

Gas and ice giants, drawn from their chemistry

Every giant in the game is procedural. Its type sets the chemistry, the chemistry sets the colours and the clouds, and a seed of its own grows the weather, so no two giants of a type are the same.

Gas and ice giants

41 kinds of giant, sorted by what you see

In the game

We classify every giant by what a pilot sees: gas or ice giant first, then a family by temperature, then whatever colours or hides its cloud (trace chemistry, haze, dayside heat or the heat from inside), then its weather. Our own generator grows each planet's weather from that type and a seed of its own, so every giant is its own world. The wall below shows every type as the generator draws it.

A rose-banded gas giant lit from the right, seen from above the plane of its broad pale rings, the planet's shadow cutting a dark band across the rings behind it, against a starfield — In Pax Abyssi: a cold gas giant around the real star 60 Leonis, its rings reaching four planetary radii and the planet's shadow falling across them.
In-game capture, Pax Abyssi

Each look is a row of data that cites its science: band count and colour, storms, haze and how the limb darkens. The generator reads the row and a seed of the planet's own, then stirs the cloud bands through a wind field built for that planet over forty steps: zonal jets after Ingersoll 2004, anticyclonic zones and cyclonic belts, vortex streets between the jets, Saturn's hexagon as a polar wave of order six and Juno's polar cyclones.

Ammonia ice sits at about 0.7 bar over ammonium hydrosulfide at about 2 bar; limb darkening follows Minnaert under a scattering haze, and the terminator fades the way it does in Cassini's frames. Hot giants lock one face to their star where Gladman 1996 says they must, and the hottest glow from their own heat. Fly down and the cloud tops resolve to 0.21 kilometres a texel on a Jupiter.

The best-known older scheme, Sudarsky's five classes of 2000, sorts gas giants by temperature alone. Ours follows the same sequence of clouds and adds the questions that decide the look; The colours of the giants maps every one of our subtypes to its nearest Sudarsky class.

Families: 5; cold, temperate, hot, and two of iceSim
Types: 41; by colouring agent, then weatherSim
Looks on the wall: 61; and a seed of its own for every planetSim
Close in: 0.21km; a texel at the cloud topsSim

The same kind of planet grown procedurally: cream zones and brown belts with finely streaked edges and hooked festoons curling into the white equatorial zone. — In Pax Abyssi: a Turbulent cold gas giant (GGC-AB-TU). Drag to compare our painted map with the planet our generator grows.

A cream and brown banded gas giant, a broad white equatorial zone with brown hooks curling into it, smooth and softly painted. — In Pax Abyssi: a Turbulent cold gas giant (GGC-AB-TU). Drag to compare our painted map with the planet our generator grows.

From painted maps to grown worlds

Our first simulator dressed each giant in a painted map, matched to our research on its type. The detail was beautiful, but a map always looks the same, and it softens and breaks down as you fly closer.

Procedural planets promise endless variety and usually deliver sameness. So we made the generator grow every feature the painted maps had: belts, festoons, hooked vortices, great spots, polar hexagons and haze, each matched to its painted original. Now every giant is its own world, and you can skim the cloud tops with the detail holding. On rocky worlds the same approach lets you fly from orbit to the ground in one unbroken descent, and walk the whole planet.

In Pax Abyssi: every sphere below is a render from the game's gas giant generator, lit from the same angle near full phase. Hover for a planet's name, and select it to turn it as a globe.