Science // Greenhouse worlds

Greenhouse worlds, from the cloud tops down

Rocky planets smothered by their own air, Venus's kind. They are the first procedural worlds in Pax Abyssi with a thick atmosphere, and each is built from its own science: a deck of cloud drawn from its winds and chemistry, tens of bar of air beneath it, and ground you can fly down to.

01 // In flight

Greenhouse worlds as you see them from the seat

In the game458 planets, all landable

Frames from the game, the HUD off, each lit by its own star at its true colour. The decks turn: their winds carry the cloud round the planet far faster than the ground beneath it. Select a frame to see it full size.

A planet of dark smoke torn open over orange and gold glowing ground fills the right of the frame, a thin grey crescent moon at lower left — HYG 67063 II, a thermal emission greenhouse world round an F7 star: its ground at 1,090 K glows through the gaps in its smoke, right round to the night side. One of its two moons hangs at lower left.
In-game capture, pre-alpha, HUD off

A grey cratered moon, half lit, passing in front of a planet so that only a ring of glowing orange cloud shows around it — HYG 67063 II's inner moon passing in front of it: a barren rock 2,400 km across, lit by the star and ringed by the glow of the planet behind.
In-game capture, pre-alpha, HUD off

A white planet as a broad crescent filling the right of the frame, its night side a black disc cut out of a blue nebula — HYG 106065 IV, an opaque water-cloud greenhouse world, as a crescent. Its night side is a silhouette against a blue nebula in the backdrop.
In-game capture, pre-alpha, HUD off

An orange planet streaked with paler tan bands across its middle, a small grey cratered moon low at the right — HYG 82119 II, a banded sulfuric acid world, its deck streaked east to west by winds far faster than the ground turns, with the larger of its two moons.
In-game capture, pre-alpha, HUD off

A salmon-orange planet at half phase on the left, soft pale streaks across its lower half, a small grey moon high on the right — HYG 76097 I, a thick acid haze world with the deck of Venus, and its moon. The terminator is soft because the light is scattered deep in the haze.
In-game capture, pre-alpha, HUD off

An olive and pale yellow planet streaked diagonally with darker green bands, a small cluster of stars to its left — HYG 11755 IV, a sulfur-dominant greenhouse world: unbroken olive and yellow haze drawn into long streaks by its winds.
In-game capture, pre-alpha, HUD off

A planet of glowing orange cloud and dark smoke on the left third, red and grey filaments of a nebula behind it on the right — HYG 67063 II against a red nebula in the backdrop. Thermal emission worlds are the commonest greenhouse worlds in the catalogue, 218 of the 458.
In-game capture, pre-alpha, HUD off

02 // Three layers

A deck, an ocean of air, and the ground

A thick atmosphere cannot be painted onto a sphere. Each greenhouse world is built in three layers, each from the planet's own science, and the descent passes through all of them.

The deck

30 to 85 km up

The face you meet from orbit: a layer of cloud whose pattern is the wind's and whose colour is the chemistry's. Water cloud is white, sulfuric acid cream to salmon, sulfur gold to olive. It breaks where the planet's own cloud cover falls short, and on the hottest worlds its gaps glow.

The air

16 to 250 bar

Carbon dioxide between the deck and the ground, so deep that the blue is scattered away above you. What reaches the ground is a dim orange light from the whole sky at once, a few per cent of the sunlight on the cloud tops.

The ground

300 to 1,400 K

A Venus surface: lava plains crossed by wrinkle ridges, broad low shields, pancake domes and few craters. On the thermal emission worlds the rock is hot enough to glow at its own temperature.

In the gamethe deck from orbit, the descent, the groundIn the gameglowing ground on the hottest worldsIn developmentthe deck lit red from belowPlannedthe scientific look

03 // Every planet its own

The deck follows the planet's science

Each look starts from our painted study of its type, and the colours are that painting's, measured, never picked. Then every planet moves the look by its own numbers. Where a planet sits within its type on surface heat, pressure, the wind at its cloud tops, sulfur dioxide and spin decides its dials: a fast wind draws long streaks and chevrons, a slow turner opens wide gaps, more sulfur greys the smoke.

The cloud cover is the planet's own, so one water world is nearly whole and the next is broken half open. The deck stands where the planet's own temperature profile puts it, its base where sulfuric acid condenses and its top where the air cools to 250 K, and it turns at the speed of the wind at the cloud tops, as Venus's does every four days.

On a thermal emission world the light in the gaps is the ground's own heat, its colour moved along Planck's law from the type's typical heat, about 1,060 K, to the planet's own. A cooler world glows deep red, the hottest gold.

Below the deck the rock glows too, by the same law, at the true ratio to the daylight that reaches it. These worlds sit far closer to their stars than Venus does, so by day the glow matters on the hottest of them and outshines the daylight on a few; on the night side it is the only light, a dark red plain at the median heat. There are 458 greenhouse planets around the catalogue stars, in 404 systems, and you can land on every one.

04 // Every look

8 types, 12 looks, sorted by what the cloud is made of

In the game8 types in the game

We sort greenhouse worlds by chemistry first, then by how much of the sky the deck covers. A type whose study we painted twice has two looks, and each planet wears the one painted for it.

In Pax Abyssi: every sphere is the game's own frame of a planet wearing that look, from its fast-travel stop 40 degrees from its star. Hover or focus a tile for its name.

In the game
In development
Planned

Thermal emission worlds

2 looks · 2 in the game

The hottest greenhouse worlds, their ground at 850 to 1,400 K under a median 57 bar of air: rock hot enough to glow, seen through the gaps in a deck of dark smoke. The commonest greenhouse world in the catalogue, 218 planets, and on the night side the glow is the only light.

TGW-TE-GL-1
TGW-TE-GL-2

Water cloud worlds

3 looks · 3 in the game

Where the air still holds more than 500 parts per million of water, the deck is water cloud: white billows broken over a slate-blue lower haze, or an unbroken pearl. They turn slowest of all, most of them once in about half a year.

TGW-WP-WS-1
TGW-WP-WS-2
TGW-WF-OQ-1

Sulfuric acid worlds

5 looks · 5 in the game

Venus's own class: a deck of sulfuric acid droplets 40 to 70 km up, cream to salmon, its pattern drawn by winds that circle the planet far faster than the ground turns. Banded where the deck is thin enough for the wind to streak it, patchy where it breaks.

TGW-AF-TK-1
TGW-AF-TK-2
TGW-AF-BN-1
TGW-AF-BN-2
TGW-AP-PT-1

Sulfur worlds

2 looks · 2 in the game

With more than 300 parts per million of sulfur dioxide in the air, sulfur colours the deck: olive and yellow haze when it is whole, gold billows over a near-black haze when it breaks. The rarest greenhouse worlds in the catalogue.