Give every body the period it is drawn going round in, and say where its orbit comes from

Audit #38: Europa's card listed its axis, eccentricity and inclination but no period, while the
scene turned it round Jupiter all the same: heliocentricPeriodDays refused every moon, since the
catalogue carried no planet masses.

Every solar-system body's period is now 360 over the JPL mean motion that carries it round the
scene, filed under Measured since that is JPL's published figure: Europa 3.55 d, the Moon 27.3 d,
Saturn 29.5 yr on the live cards, Earth 365.2564 d. heliocentricPeriodDays is gone. Exoplanets
keep the archive's period, or none.

The card's provenance line now ends with where the orbit comes from, "Orbit: JPL SSD satellite
mean elements, epoch 1997 Jan 16." for Europa, "Orbit: JPL approximate mean elements (Standish),
fit for 3000 BC to AD 3000." for a planet, and the Sun's system note says so too: "Orbits
propagated from JPL mean elements, the planets' fit for 3000 BC to AD 3000, to the current
date." Other systems keep "published elements". All three read in the running app.

Each has a test that fails without it (moons refused a period, provenance without the orbit, a
note without the source).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/app/features/galaxy-system/galaxy-system-scene.component.spec.ts

@@ -831,6 +831,19 @@ describe('GalaxySystemSceneComponent camera-flight transitions', () => {
     expect(navigationStore.viewLevel()).toBe('system');
   });
 
+  it('says where a system’s orbits come from, and for the Sun how long they hold', async () => {
+    const note = (): string => (fixture.componentInstance as unknown as { hudNote: () => string }).hudNote();
+    navigationStore.selectStar(SUN.id);
+    await flushAsync();
+    await advanceFrames(engine, 2.5);
+    expect(note()).toBe('Orbits propagated from JPL mean elements, the planets’ fit for 3000 BC to AD 3000, to the current date.');
+
+    navigationStore.selectStar(ALPHA_CENTAURI.id);
+    await flushAsync();
+    await advanceFrames(engine, 5);
+    expect(note()).toBe('Orbits propagated from published elements to the current date.');
+  });
+
   it('performs the floating-origin recenter: the camera lands close to the AU-space origin, not out at parsec-scale coordinates', async () => {
     navigationStore.selectStar(ALPHA_CENTAURI.id);
     await flushAsync();

src/app/features/galaxy-system/galaxy-system-scene.component.ts

@@ -1760,7 +1760,10 @@ export class GalaxySystemSceneComponent implements AfterViewInit, OnDestroy {
           ? [{ label: 'Luminosity', value: formatLuminosity(luminosity), derived: true }]
           : []),
       ]);
-      this.hudNote.set(this.time.atNow() ? 'Orbits propagated from published elements to the current date.' : 'Orbits propagated from published elements to the date on the clock.');
+      // Where the orbits come from, and for the Sun how far from the present they hold: each
+      // body's card names its own source and epoch.
+      const source = this.bodies.some((body) => body.systemStarId === star.id) ? 'JPL mean elements, the planets’ fit for 3000 BC to AD 3000,' : 'published elements';
+      this.hudNote.set(`Orbits propagated from ${source} to ${this.time.atNow() ? 'the current date' : 'the date on the clock'}.`);
       this.hudRange.set(
         formatAu(
           this.engine.visibleHalfHeight(