Derive a surface for every body that was never photographed

Fifteen bodies here have a real photograph. Every exoplanet does not, and
never will on current instruments — none has ever been imaged — and nor do
several of the solar system's own moons. Those all shared one crude
stand-in: a few noisy bands tinted by category, cached per colour, so
every exoplanet in the app was literally the same picture.

They now get a surface reasoned from what has actually been measured.

The chain is standard at every link. A host star's luminosity comes from
its catalogued apparent magnitude and its parallax distance — that pair is
exactly an absolute magnitude — plus a bolometric correction for its
spectral class. The correction is not optional: an M dwarf radiates most
of its light in the infrared, so its visual magnitude understates it more
than tenfold, and M dwarfs are what most nearby planet hosts are.
Luminosity and the semi-major axis then give an equilibrium temperature,
mass and radius give a bulk density, and size, temperature and density
together give a class of world.

Checked against the solar system the temperatures land on Earth 255 K,
Jupiter 112 K, Neptune 46 K, all within a kelvin or two of published
values, and 51 Pegasi b comes out at 1227 K against a published 1200.

Each class carries a palette reasoned from its chemistry — methane absorbs
red light, which is why the ice giants are blue — and a structure: zonal
bands for a body with a fluid envelope, because a rapidly rotating
atmosphere organises into them, and fractal terrain for one with a solid
surface. Polar caps grow and shrink with the derived temperature, which is
the clearest visible consequence of the whole chain.

The generator samples three-dimensional noise along the sphere rather than
a flat field, so there is no seam to stitch at the antimeridian and no
pinching at the poles, and it writes into a byte array rather than a
canvas — a pure function, testable, with no 2D context to be unavailable.

Two things the derivation cannot do, both stated on screen next to the
measurements it rests on. Equilibrium temperature ignores greenhouse
warming and internal heat, so Venus comes out at 300 K against a real
surface of 737 K and Io, kept molten by tides, classifies as ice. And
these are illustrations: reasoned, but not observations.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaySiNst4HhDXBHnMy8p5G

src/app/features/body-detail/body-detail-scene.component.ts

@@ -6,8 +6,12 @@ import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
 
 import { DataLoaderService } from '../../core/data/data-loader.service';
 import { EngineService } from '../../core/engine/engine.service';
+import { appearanceForBody, appearanceForExoplanet } from '../../shared/astro/body-appearance';
+import { EARTH_RADIUS_KM } from '../../shared/astro/planet-appearance';
+import { luminositySolar } from '../../shared/astro/stellar';
+import { planetTexture } from '../../shared/rendering/procedural-planet-texture';
 import { applyMilkyWaySkybox, createGlowSprite } from '../../shared/rendering/skybox';
-import { atmosphereColorFor, bodyTexturePath, loadCachedTexture, MILKY_WAY_SKYBOX_PATH, proceduralBodyTexture, SATURN_RING_TEXTURE_PATH } from '../../shared/rendering/texture-catalog';
+import { atmosphereColorFor, bodyTexturePath, loadCachedTexture, MILKY_WAY_SKYBOX_PATH, SATURN_RING_TEXTURE_PATH } from '../../shared/rendering/texture-catalog';
 import { BodyRecord } from '../../shared/models/body.model';
 import { ExoplanetRecord } from '../../shared/models/exoplanet.model';
 import { StarRecord } from '../../shared/models/star.model';
@@ -15,13 +19,6 @@ import { NavigationStore } from '../../shared/state/navigation.store';
 import { BodyDetailViewModel } from './body-detail.model';
 import { InfoPanelComponent } from './info-panel.component';
 
-const KIND_COLORS: Record<BodyDetailViewModel['kind'], THREE.ColorRepresentation> = {
-  planet: 0x8cbfff,
-  moon: 0xbfbfbf,
-  dwarf: 0xccb28c,
-  exoplanet: 0xd966d9
-};
-
 /** Gas giants read as smoother/less rocky than terrestrial bodies under the same lighting rig. */
 const GAS_GIANT_IDS = new Set(['jupiter', 'saturn', 'uranus', 'neptune']);
 const GLOW_SCALE = 2.6;
@@ -131,19 +128,24 @@ export class BodyDetailSceneComponent implements AfterViewInit, OnDestroy {
         kind: body.kind,
         hostStarName: hostStar?.name ?? 'Unknown star',
         radiusKm: body.radiusKm,
-        orbit: body.orbit
+        orbit: body.orbit,
+        appearance: appearanceForBody(body, this.bodies, this.luminosityOf(hostStar)),
+        hasPhotography: bodyTexturePath(body.id) !== undefined
       });
       this.navigationStore.selectStar(body.systemStarId);
     } else if (exoplanet) {
+      const hostStar = this.stars.find((star) => star.id === exoplanet.hostStarId);
       this.viewModel.set({
         id: exoplanet.id,
         name: exoplanet.name,
         kind: 'exoplanet',
         hostStarName: exoplanet.hostStarName,
-        radiusKm: exoplanet.radiusEarth ? exoplanet.radiusEarth * 6371 : undefined,
+        radiusKm: exoplanet.radiusEarth ? exoplanet.radiusEarth * EARTH_RADIUS_KM : undefined,
         massEarth: exoplanet.massEarth,
         discoveryYear: exoplanet.discoveryYear,
-        orbit: exoplanet.orbit
+        orbit: exoplanet.orbit,
+        appearance: appearanceForExoplanet(exoplanet, this.luminosityOf(hostStar)),
+        hasPhotography: bodyTexturePath(exoplanet.id) !== undefined
       });
       if (exoplanet.hostStarId !== null) {
         this.navigationStore.selectStar(exoplanet.hostStarId);
@@ -161,20 +163,33 @@ export class BodyDetailSceneComponent implements AfterViewInit, OnDestroy {
     }
   }
 
+  /**
+   * The host star's luminosity in solar units, from its own catalogued magnitude and distance.
+   * `null` for an exoplanet whose host never cross-referenced to the star catalogue, which
+   * leaves its planets with no derived temperature rather than a guessed one.
+   */
+  private luminosityOf(star: StarRecord | undefined): number | null {
+    if (!star) {
+      return null;
+    }
+    return luminositySolar({ magnitude: star.magnitude, distancePc: Math.hypot(star.x, star.y, star.z), spectralType: star.spectralType });
+  }
+
   private applyViewModelToScene(): void {
     const viewModel = this.viewModel();
     if (!viewModel || !this.planetMaterial) {
       return;
     }
 
+    // Real photography wherever it exists, and a surface derived from the body's own measured
+    // properties wherever it does not — which is every exoplanet, since none has ever been
+    // imaged, and the handful of moons no probe returned a usable map of.
     const realTexturePath = bodyTexturePath(viewModel.id);
-    const texture = realTexturePath ? loadCachedTexture(realTexturePath) : proceduralBodyTexture(KIND_COLORS[viewModel.kind]);
-    this.planetMaterial.map = texture ?? null;
-    // A texture (real photo or procedural stand-in) supplies its own color; a plain white base
-    // keeps that color true instead of tinting it through `KIND_COLORS` a second time. If no
-    // texture is available at all (e.g. canvas rendering unsupported), fall back to the flat kind color.
-    this.planetMaterial.color.set(texture ? 0xffffff : KIND_COLORS[viewModel.kind]);
-    this.planetMaterial.roughness = GAS_GIANT_IDS.has(viewModel.id) ? 0.55 : 0.85;
+    this.planetMaterial.map = realTexturePath ? loadCachedTexture(realTexturePath) : planetTexture(viewModel.appearance);
+    // The texture supplies its own colour, so the base stays white rather than tinting it twice.
+    this.planetMaterial.color.set(0xffffff);
+    // A fluid envelope scatters light more evenly than a solid surface does.
+    this.planetMaterial.roughness = GAS_GIANT_IDS.has(viewModel.id) || viewModel.appearance.palette.structure === 'banded' ? 0.55 : 0.85;
     this.planetMaterial.needsUpdate = true;
 
     this.disposeRing();
@@ -275,7 +290,9 @@ export class BodyDetailSceneComponent implements AfterViewInit, OnDestroy {
     const geometry = new THREE.SphereGeometry(1, 64, 48);
     const viewModel = this.viewModel();
     this.planetMaterial = new THREE.MeshStandardMaterial({
-      color: viewModel ? KIND_COLORS[viewModel.kind] : 0xffffff,
+      // White, always: the map that arrives a moment later carries the colour, whether it is a
+      // photograph or a surface derived from the body's own measurements.
+      color: 0xffffff,
       roughness: 0.85,
       metalness: 0.05
     });