diff --git a/src/app/features/body-detail/body-view-model.spec.ts b/src/app/features/body-detail/body-view-model.spec.ts
index 999d6dd..bf5315a 100644
--- a/src/app/features/body-detail/body-view-model.spec.ts
+++ b/src/app/features/body-detail/body-view-model.spec.ts
@@ -74,6 +74,12 @@ describe('buildBodyViewModel', () => {
     expect(bodyReadouts(model).measured.find((row) => row.label === 'Inclination')?.value).toBe('0.00°');
   });
 
+  it('prints the eccentricity measured for a moon whose orbit keeps an older one', () => {
+    const hyperion: BodyRecord = { ...luna, id: 'hyperion', orbit: orbit({ eccentricity: 0.0232 }), measuredEccentricity: 0.105 };
+    const model = buildBodyViewModel('hyperion', { ...catalogues, bodies: [earth, hyperion] })!;
+    expect(bodyReadouts(model).measured.find((row) => row.label === 'Eccentricity')?.value).toBe('0.105');
+  });
+
   it('says where the orbit comes from, in the card’s provenance', () => {
     expect(bodyReadouts(buildBodyViewModel('luna', catalogues)!).provenance).toContain('Orbit: JPL SSD satellite mean elements, epoch 2000 Jan 1.');
   });
diff --git a/src/app/features/body-detail/body-view-model.ts b/src/app/features/body-detail/body-view-model.ts
index 9df6c18..f7b562c 100644
--- a/src/app/features/body-detail/body-view-model.ts
+++ b/src/app/features/body-detail/body-view-model.ts
@@ -52,7 +52,7 @@ export function buildBodyViewModel(id: string, catalogues: BodyCatalogues): Body
       hostStarName: hostStar?.name ?? 'Unknown star',
       hostStarId: body.systemStarId,
       radiusKm: body.radiusKm,
-      orbit: body.orbit,
+      orbit: body.measuredEccentricity === undefined ? body.orbit : { ...body.orbit, eccentricity: body.measuredEccentricity },
       appearance: appearanceForBody(body, catalogues.bodies, luminosityOf(hostStar)),
       hasPhotography: bodyTexturePath(body.id) !== undefined,
       orbitalPeriodDays: periodDays,
diff --git a/src/app/shared/models/body.model.ts b/src/app/shared/models/body.model.ts
index d1a53ae..aa607ea 100644
--- a/src/app/shared/models/body.model.ts
+++ b/src/app/shared/models/body.model.ts
@@ -63,6 +63,13 @@ export interface BodyRecord {
   laplacePole?: { raDeg: number; decDeg: number };
   /** Where the elements come from and the span they hold over, as the card prints it. */
   orbitSource: string;
+  /**
+   * The eccentricity the card prints, where it is not the orbit's own: Hyperion's row in the table
+   * its orbit is drawn from gives 0.0232, under a quarter of the 0.105 JPL's current table (SAT441)
+   * and Horizons (0.074 to 0.132 from 1980 to 2100) give. The older row still places Hyperion
+   * nearer where Horizons has it than the same row with 0.105 does, so the orbit keeps it.
+   */
+  measuredEccentricity?: number;
   /**
    * For `kind: 'moon'`, the `id` of the planet it orbits — its `orbit` is expressed
    * relative to that planet, not heliocentrically. Undefined for planets/dwarfs.
diff --git a/src/assets/data/bodies.json b/src/assets/data/bodies.json
index 7ff2a89..78c0544 100644
--- a/src/assets/data/bodies.json
+++ b/src/assets/data/bodies.json
@@ -1512,6 +1512,7 @@
       "decDeg": 83.862
     },
     "orbitSource": "JPL SSD satellite mean elements, epoch 2000 Jan 1",
+    "measuredEccentricity": 0.105,
     "parentBodyId": "saturn"
   },
   {
diff --git a/tools/etl/build.ts b/tools/etl/build.ts
index e6908d6..cefeb76 100644
--- a/tools/etl/build.ts
+++ b/tools/etl/build.ts
@@ -145,6 +145,8 @@ function validateMerge(stars: StarRecord[]): void {
  * 0.9.
  */
 const MAX_PLANET_OFFSET_DEG = 0.25;
+/** Measured on this catalogue: at most 0.0151 (Phoebe and the Moon) once Hyperion prints its current 0.105. */
+const MAX_ECCENTRICITY_OFFSET = 0.03;
 const MAX_MOON_OFFSET_DEG = 2.5;
 const KM_PER_AU = 149597870.7;
 const DEG_TO_RAD = Math.PI / 180;
@@ -259,6 +261,13 @@ function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, Orbita
       `${body.name}'s mean elements put it ${offset.toFixed(2)} degrees from where Horizons has it (at most ${ceiling} expected) — the elements were read wrongly.`
     );
     offsets.push(`${body.id} ${offset.toFixed(3)}`);
+    // The card prints this under "Measured". An osculating eccentricity swings about its mean — the
+    // Moon's by 0.015 here, Phoebe's by as much — but not by the 0.087 Hyperion's older row was out.
+    const printed = body.measuredEccentricity ?? body.orbit.eccentricity;
+    assertCondition(
+      Math.abs(printed - horizons!.eccentricity) <= MAX_ECCENTRICITY_OFFSET,
+      `${body.name}'s card gives an eccentricity of ${printed}, where Horizons' osculating orbit has ${horizons!.eccentricity.toFixed(4)} (at most ${MAX_ECCENTRICITY_OFFSET} apart expected).`
+    );
 
     // A radius of 0 is what a page whose radius no pattern reads comes out as — Charon's did.
     assertCondition(body.radiusKm > 0, `Body ${body.id} has no radius; its page states it in a form the ETL does not read.`);
diff --git a/tools/etl/fetchSolarSystem.ts b/tools/etl/fetchSolarSystem.ts
index 8b0d1ef..6a635ee 100644
--- a/tools/etl/fetchSolarSystem.ts
+++ b/tools/etl/fetchSolarSystem.ts
@@ -33,6 +33,8 @@ interface BodySpec {
   radiusKm?: number;
   /** A measured sidereal day, in hours, where a later measurement overturns the one its source gives. */
   rotationPeriodHours?: number;
+  /** The eccentricity for the card, where the row the orbit is drawn from gives an outdated one; see `BodyRecord.measuredEccentricity`. */
+  measuredEccentricity?: number;
   /** A moon that does not keep one face to its planet: its page's own spin, or none, is kept. */
   spinsFreely?: boolean;
   /** A moon heavy enough to move its planet round their barycentre visibly; see `BodyRecord.massRatio`. */
@@ -111,7 +113,8 @@ const BODY_SPECS: BodySpec[] = [
   { id: 'rhea', name: 'Rhea', kind: 'moon', horizonsCommand: '605', center: '500@699', parentBodyId: 'saturn' },
   { id: 'titan', name: 'Titan', kind: 'moon', horizonsCommand: '606', center: '500@699', parentBodyId: 'saturn' },
   // Hyperion tumbles ("Rotational period = Chaotic") and Phoebe, captured, turns in 9.27 hours.
-  { id: 'hyperion', name: 'Hyperion', kind: 'moon', horizonsCommand: '607', center: '500@699', parentBodyId: 'saturn', spinsFreely: true },
+  // Hyperion's eccentricity is 0.105 in JPL's current table (ssd.jpl.nasa.gov/sats/elem, SAT441).
+  { id: 'hyperion', name: 'Hyperion', kind: 'moon', horizonsCommand: '607', center: '500@699', parentBodyId: 'saturn', spinsFreely: true, measuredEccentricity: 0.105 },
   { id: 'iapetus', name: 'Iapetus', kind: 'moon', horizonsCommand: '608', center: '500@699', parentBodyId: 'saturn' },
   // Phoebe's row gives a mean motion of 0.6569114 degrees a day, a 548.02-day year, where its
   // Horizons page and JPL's current table (SAT441) give 550.30: the table's own note warns that
@@ -232,6 +235,7 @@ export async function fetchSolarSystem(): Promise<{ bodies: BodyRecord[]; horizo
       rates: mean.rates,
       ...(mean.laplacePole ? { laplacePole: mean.laplacePole } : {}),
       orbitSource: mean.orbitSource,
+      ...(spec.measuredEccentricity !== undefined ? { measuredEccentricity: spec.measuredEccentricity } : {}),
       ...(spec.parentBodyId ? { parentBodyId: spec.parentBodyId } : {}),
       ...(parentGm !== undefined ? { massRatio: result.gmKm3PerS2! / parentGm } : {}),
       ...(rotationPeriodHours !== undefined ? { rotationPeriodHours } : {}),