Alien-scapes
Procedurally generated landscapes under other suns, where every colour on
screen is computed from a spectrum rather than chosen by hand.
Pick a star, an exoplanet and an atmosphere, and the page works out what the sky,
the ground, the water and — if anything can live there — the vegetation would
actually look like. Then it shows you the spectra behind that answer and lets you
export the whole thing as a data sheet.
→ Open Alien-scapes
No build step, no dependencies, no network calls. It is a handful of ES modules
and a canvas.
What it does
- 14 stellar presets on a spectral-class grid (O–M, dwarfs and giants) plus
28 more named stars including Wolf-Rayet, white dwarf and brown dwarf
classes — and a free temperature slider from 1,000 K to 50,000 K.
- 15 exoplanet presets — Earth, Mars, Venus and Titan as controls, then
TRAPPIST-1 e, Proxima b, Kepler-186 f, LHS 1140 b, TOI-700 d, K2-18 b,
Kepler-452 b, GJ 667 C c, GJ 1214 b, Gliese 581 g, and the circumbinary
Kepler-16 (AB) b, which really does have two suns in the sky.
- 10 atmospheres, from airless through Earth Rayleigh, Mars dust, Venus acid
cloud, Titan tholin haze, methane-rich and hycean.
- Leaf colours per spectral type, derived from a pigment model rather than a
lookup table — including the purple result for a retinal biosphere.
- Three charts: the surface spectrum, the pigment absorption curves
(retinal, chlorophyll and the nitroplast antenna, plus whatever the model
selected), and the resulting leaf reflectance with its red edge marked.
- Export to PNG, JPG or PDF as a full data sheet — the landscape plus every
number behind it — or the landscape on its own.
How the colours are computed
Nothing here is art-directed. Each colour is the result of an integral.
Starlight
The star is treated as a blackbody at its effective temperature. Planck's law
gives the emitted spectrum, an atmospheric transmission profile attenuates it,
and the result is integrated against the CIE 1931 2° standard observer to get
tristimulus XYZ, then converted to sRGB through the D65 primaries and the sRGB
transfer function. This path is ported from
starlight-filter, which uses
the same integral to drive a display's gamma ramp.
Because Beer's law is exponential in path length, a lower star simply means the
zenith transmission raised to the air mass. That one relationship is why the same
model produces a blue noon and a red sunset without being told about either.
Sky, ground and water
A Rayleigh atmosphere scatters short wavelengths out of the beam, so the sky
glows with exactly what the beam lost. Dust and haze absorb rather than
scatter, so those skies take the transmitted tint instead of its complement —
which is why Mars is butterscotch rather than blue.
Ground colour is the total downwelling light (direct beam plus skylight) times
a mineral reflectance curve, integrated the same way. Out-of-gamut results are
tone-mapped on luminance with the chromaticity preserved, so a deep Rayleigh sky
comes out pale blue instead of clipping to flat white.
Vegetation
Photosynthesis is a quantum process, so the model counts photons, not energy.
A reaction-centre pigment is chosen by weighing three things against each other:
- Capture — how many arriving photons the absorption curve takes.
- Thermalisation — every captured photon is worth
1/λ_trap, because
energy above the trap is dumped as heat. This is what stops far-red pigments
winning under every star.
- Cost — a pigment absorbing everywhere is metabolically expensive.
Antenna pigments are then layered on, constrained by what can physically attach
to what: a chlorophyll photosystem accepts chlorophyll b, carotenoids and
phycobiliproteins, while a rhodopsin accepts only a carotenoid and
bacteriorhodopsin runs bare. Phycobiliproteins carry a heavy cost penalty because
a phycobilisome can run to half a cell's protein — which is why land plants never
took that option, and without it the model paints Earth's forests red.
The leaf's reflectance is what survives that absorption, scaled by a structural
reflectance term that reproduces the red edge. Its colour is the illuminant
times that reflectance. Calibration check: Earth under the Sun comes out green,
reflectance peaking near 550 nm with a red edge at ~705 nm, which is what real
vegetation does.
Honesty about the model
This is a worldbuilding and teaching tool, not a radiative-transfer code.
- Pigment absorption curves are sums of Gaussians placed at literature peak
positions. The peak positions are real; the band shapes are modelled, not
digitised from measured spectra.
- Stellar luminosities and radii are rounded literature values, good enough
to place a planet in or out of a habitable zone and no more.
- Habitable-zone bounds use the Kopparapu et al. (2013) runaway-greenhouse
and maximum-greenhouse coefficients, which are fitted for 2600–7200 K. Outside
that range the UI says the bounds are extrapolated.
- Atmospheric transmission profiles are deliberately simple — enough to
reproduce each world's characteristic tint, not to model its chemistry.
- The nitroplast needs its own caveat. The nitroplast is a nitrogen-fixing
organelle, derived from the cyanobacterium UCYN-A inside the alga
Braarudosphaera bigelowii. It has lost photosystem II and RuBisCO, so it does
not fix carbon. The curve here models the photosystem I antenna it still
carries — what the organelle still absorbs, not a carbon-fixing pigment.
- Equilibrium temperatures use a greenhouse offset per atmosphere rather than
a climate model. As a sanity check the Earth preset lands on 288 K and Venus on
727 K, against real values of 288 K and 737 K.
The reasoning behind the leaf-colour model follows Kiang et al. (2007),
Spectral signatures of photosynthesis.
Running it locally
There is nothing to install, but the page uses ES modules, so it needs to be
served over HTTP rather than opened from the filesystem:
python -m http.server 8123
Then open http://localhost:8123.
Layout
| File | What lives there |
|---|
src/cie.js | CIE 1931 CMF table, Planck's law, XYZ → sRGB, tone mapping |
src/stars.js | Stellar presets, habitable zone, angular diameter, insolation |
src/planets.js | Atmospheric transmission, exoplanet presets, biome classifier |
src/pigments.js | Pigment spectra, suite selection, leaf reflectance solver |
src/scene.js | Ties it together — every derived quantity and colour |
src/landscape.js | The procedural renderer; shape only, no physics |
src/charts.js | Spectrum, absorption and reflectance charts |
src/exporter.js | Data sheet composition, PNG/JPG, and a hand-rolled PDF writer |
src/noise.js | Seeded PRNG and fBm |
src/main.js | UI wiring |
fonts/ | Atkinson Hyperlegible Next, self-hosted (SIL OFL 1.1, see fonts/OFL.txt) |
Seeds are deterministic: the same seed always redraws the same terrain at any
resolution, so an exported sheet can be reproduced exactly.
Licence
MIT.
