diff --git a/Assets/Prefabs/RPG/Planets/Gas Giant.prefab b/Assets/Prefabs/RPG/Planets/Gas Giant.prefab
index 46ae7a3b1..cb628d804 100644
--- a/Assets/Prefabs/RPG/Planets/Gas Giant.prefab	
+++ b/Assets/Prefabs/RPG/Planets/Gas Giant.prefab	
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diff --git a/Assets/Prefabs/RPG/Planets/Sun.prefab b/Assets/Prefabs/RPG/Planets/Sun.prefab
index a7950f448..cf7fb216f 100644
--- a/Assets/Prefabs/RPG/Planets/Sun.prefab
+++ b/Assets/Prefabs/RPG/Planets/Sun.prefab
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diff --git a/Assets/Resources/Settings.asset b/Assets/Resources/Settings.asset
index 032d8c898..64c4333d7 100644
--- a/Assets/Resources/Settings.asset
+++ b/Assets/Resources/Settings.asset
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:667368f42385152984589abb3803aa88a51937286ac2450d890970710ec38e37
-size 13039
+oid sha256:319895214aaeea5d4dfe034c46edca055f62c6b4a9692788e60ce8a5827c4b78
+size 12634
diff --git a/Assets/Scenes/ARPG.unity b/Assets/Scenes/ARPG.unity
index b93a7b909..57c793e09 100644
--- a/Assets/Scenes/ARPG.unity
+++ b/Assets/Scenes/ARPG.unity
@@ -16322,7 +16322,6 @@ MonoBehaviour:
   Settings: {fileID: 11400000, guid: cd2344e2001a37544aab0960c164d4ff, type: 2}
   ZoneRoot: {fileID: 2095699057}
   SectorBrushes: {fileID: 1037490739}
-  SectorBoundaryBrush: {fileID: 1476765550}
   SceneCamera: {fileID: 887677622}
   FogCameras:
   - {fileID: 559840917}
@@ -16864,7 +16863,6 @@ Transform:
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diff --git a/Assets/Scenes/Main Menu.unity b/Assets/Scenes/Main Menu.unity
index a37cfffba..2d80e45b7 100644
--- a/Assets/Scenes/Main Menu.unity	
+++ b/Assets/Scenes/Main Menu.unity	
@@ -1061,16 +1061,6 @@ PrefabInstance:
       propertyPath: m_LocalEulerAnglesHint.z
       value: 0
       objectReference: {fileID: 0}
-    - target: {fileID: 7852221720741322892, guid: 046dde0f4600bce41ad33c476f99b309,
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-      value: 512
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-      value: 512
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         type: 3}
       propertyPath: m_LocalScale.x
diff --git a/Assets/Scenes/TestScene.unity b/Assets/Scenes/TestScene.unity
index 5288b6845..ffc3f3905 100644
--- a/Assets/Scenes/TestScene.unity
+++ b/Assets/Scenes/TestScene.unity
@@ -911,16 +911,6 @@ PrefabInstance:
       propertyPath: m_LocalEulerAnglesHint.z
       value: 0
       objectReference: {fileID: 0}
-    - target: {fileID: 7852221720741322892, guid: 046dde0f4600bce41ad33c476f99b309,
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-      value: 40
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-        type: 3}
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-      value: 40
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     - target: {fileID: 7852221720969441490, guid: 046dde0f4600bce41ad33c476f99b309,
         type: 3}
       propertyPath: m_LocalScale.x
@@ -1778,16 +1768,6 @@ PrefabInstance:
       propertyPath: m_LocalEulerAnglesHint.z
       value: 0
       objectReference: {fileID: 0}
-    - target: {fileID: 7852221720741322892, guid: 046dde0f4600bce41ad33c476f99b309,
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-      value: 40
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-      value: 40
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@@ -5297,16 +5277,6 @@ PrefabInstance:
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       value: 0
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-      value: 40
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-      value: 40
-      objectReference: {fileID: 0}
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         type: 3}
       propertyPath: m_LocalScale.x
diff --git a/Assets/Scripts/Gameplay/GameSettings.cs b/Assets/Scripts/Gameplay/GameSettings.cs
index d2b3df1d8..65e134755 100644
--- a/Assets/Scripts/Gameplay/GameSettings.cs
+++ b/Assets/Scripts/Gameplay/GameSettings.cs
@@ -15,7 +15,6 @@ public class GameSettings : ScriptableObject
     public float HeatstrokePhasingFrequency = 5;
     public float WormholeDistanceRatio;
     public float DefaultViewDistance;
-    public float MinimapZoneGravityRange;
     public float[] MinimapZoomLevels;
     public int DefaultMinimapZoom;
     public ExponentialCurve IconSize;
diff --git a/Assets/Scripts/ServerShared/Settings.cs b/Assets/Scripts/ServerShared/Settings.cs
index 1a04dd2ae..ab422c7fa 100644
--- a/Assets/Scripts/ServerShared/Settings.cs
+++ b/Assets/Scripts/ServerShared/Settings.cs
@@ -13,15 +13,8 @@ using static CultMath.math;
 [Serializable, MessagePackObject(keyAsPropertyName:true), JsonObject]
 public class PlanetSettings
 {
-    public float ZoneDepthExponent;
-    public float ZoneDepth;
-    public float ZoneBoundaryFog;
     public ExponentialCurve GravityDepth;
     public ExponentialCurve GravityRadius;
-    public ExponentialCurve WaveDepth;
-    public ExponentialCurve WaveRadius;
-    public ExponentialCurve WaveFrequency;
-    public ExponentialCurve WaveSpeed;
     public ExponentialCurve LightRadius;
     public ExponentialCurve BodyRadius;
     public float AsteroidVerticalOffset = -5f;
diff --git a/Assets/Scripts/ServerShared/Zone.cs b/Assets/Scripts/ServerShared/Zone.cs
index 16373f147..1b3604b54 100644
--- a/Assets/Scripts/ServerShared/Zone.cs
+++ b/Assets/Scripts/ServerShared/Zone.cs
@@ -161,6 +161,12 @@ public class Zone
             Orbits.Add(orbit.Key, new Orbit(Settings, cache.Get(orbit)));
         }
 
+        // Aetheria gravity (target invariant zone-valid-before-tick): every orbit is placed at the pack's time
+        // when the zone is built, so each well, light and body pose read before the first Update is where the
+        // body is. Velocity stays zero until the first Update differences two placed positions.
+        foreach (var orbit in Orbits)
+            GetOrbitPosition(orbit.Key);
+
         foreach (var body in pack.Planets)
         {
             var planet = cache.Get(body);
@@ -266,18 +272,16 @@ public class Zone
 
     private bool IsExpired(ChunkWear wear) => wear.Damage <= 0f && (!wear.BrokenUntil.HasValue || wear.BrokenUntil.Value <= _time);
 
-    public void AddOrbit(OrbitData orbit)
-    {
-        Orbits.Add(_itemManager.ItemData.RefOf(orbit).Key, new Orbit(Settings, orbit));
-    }
-
     public void Update(float deltaTime)
     {
         _time += deltaTime;
         _updatedOrbits.Clear();
+        // Every previous position is taken before any orbit is placed: GetOrbitPosition places a parent as a
+        // side effect of placing its child, so differencing inside one loop would depend on dictionary order.
+        foreach (var orbit in Orbits)
+            orbit.Value.PreviousPosition = orbit.Value.Position;
         foreach (var orbit in Orbits)
         {
-            orbit.Value.PreviousPosition = orbit.Value.Position;
             orbit.Value.Position = GetOrbitPosition(orbit.Key);
             orbit.Value.Velocity = (orbit.Value.Position - orbit.Value.PreviousPosition) / deltaTime;
         }
@@ -591,26 +595,6 @@ public class Zone
             into[i] = beltInstance.Pose(i, _time, parentPosition, Settings, ChunkRadius(new ChunkId(belt, i)));
     }
 
-    public OrbitData CreateOrbit(CultRecordKey parent, float2 position)
-    {
-        var parentPosition = GetOrbitPosition(parent);
-        var delta = position - parentPosition;
-        var distance = length(delta);
-        var period = Settings.OrbitPeriod.Evaluate(distance);
-        var phase = atan2(delta.y, delta.x) / (PI * 2);
-        var currentPhase = frac(_time / period);
-        var storedPhase = (float) frac(phase - currentPhase);
-
-        var orbit = new OrbitData
-        {
-            Distance = distance,
-            Parent = new CultRecordRef<OrbitData>(parent),
-            Phase = storedPhase
-        };
-        Orbits.Add(_itemManager.ItemData.Upsert(orbit).Key, new Orbit(Settings, orbit));
-        return orbit;
-    }
-
     public SecurityLevel GetSecurityLevel(float2 pos)
     {
         if (GalaxyZone.Owner==null) return SecurityLevel.Open;
@@ -630,7 +614,7 @@ public class Zone
 
     public float GetHeight(float2 position)
     {
-        var result = -PowerPulse(length(position)/(Pack.Radius*2), Settings.ZoneDepthExponent) * Settings.ZoneDepth;
+        var result = 0f;
         foreach (var body in PlanetInstances.Values)
         {
             var p = position - body.Orbit.Position; //GetOrbitPosition(body.BodyData.Orbit)
@@ -641,18 +625,6 @@ public class Zone
                 var depth = body.GravityWellDepth;
                 result -= PowerPulse(sqrt(distSqr) / gravityRadius, body.BodyData.GravityDepthExponent) * depth;
             }
-
-            if (body is GasGiant gas)
-            {
-                var waveRadius = gas.GravityWavesRadius;
-                if(distSqr < waveRadius*waveRadius)
-                {
-                    var depth = gas.GravityWavesDepth;
-                    var frequency = Settings.WaveFrequency.Evaluate(body.BodyData.Mass);
-                    var speed = gas.GravityWavesSpeed;
-                    result -= RadialWaves(sqrt(distSqr) / waveRadius, 8, 1.25f, frequency, (float) (_time * speed)) * depth;
-                }
-            }
         }
 
         return result;
@@ -716,12 +688,6 @@ public class Zone
         return pow((x + 1) * (1 - x), exponent);
     }
 
-    public static float RadialWaves(float x, float maskExponent, float sineExponent, float frequency, float phase)
-    {
-        //x *= 2;
-        return PowerPulse(x, maskExponent) * cos(pow(x*2, sineExponent) * frequency + phase);
-    }
-
     public float3 GetNormal(float2 pos, float step = .1f, float mul = 1)
     {
         float hL = GetHeight(new float2(pos.x - step, pos.y)) * mul;
@@ -763,22 +729,10 @@ public class Planet
 public class GasGiant : Planet
 {
     public GasGiantData GasGiantData;
-    public float GravityWavesDepth;
-    public float GravityWavesRadius;
-    public float GravityWavesSpeed;
 
     public GasGiant(PlanetSettings settings, GasGiantData data, Orbit orbit) : base(settings, data, orbit)
     {
         GasGiantData = data;
-        CalculateProperties();
-    }
-
-    public new void CalculateProperties()
-    {
-        base.CalculateProperties();
-        GravityWavesDepth = Settings.WaveDepth.Evaluate(BodyData.Mass) * GasGiantData.WaveDepthMultiplier;
-        GravityWavesRadius = Settings.WaveRadius.Evaluate(BodyData.Mass) * GasGiantData.WaveRadiusMultiplier;
-        GravityWavesSpeed = Settings.WaveSpeed.Evaluate(BodyData.Mass) * GasGiantData.WaveSpeedMultiplier;
     }
 }
 
diff --git a/Assets/Scripts/ServerShared/ZoneData.cs b/Assets/Scripts/ServerShared/ZoneData.cs
index 7dc02b878..70448ac40 100644
--- a/Assets/Scripts/ServerShared/ZoneData.cs
+++ b/Assets/Scripts/ServerShared/ZoneData.cs
@@ -186,18 +186,6 @@ public class GasGiantData : BodyData
     [JsonProperty("albedoRotationSpeed"), Key(13)]
     public float AlbedoRotationSpeed = 1;
 
-    [JsonProperty("gravRadiusMul")] [Key(14)]
-    public float WaveRadiusMultiplier = 1;
-
-    [JsonProperty("depthMul")] [Key(15)]
-    public float WaveDepthMultiplier = 1;
-
-    [JsonProperty("depthExp")] [Key(16)]
-    public float WaveDepthExponent = 8;
-
-    [JsonProperty("depthExp")] [Key(17)]
-    public float WaveSpeedMultiplier = 8;
-
     [JsonProperty("materialOverrides"), Key(18)]
     public List<string> MaterialOverrides = new List<string>();
 
diff --git a/Assets/Scripts/Zone Display/GasGiantObject.cs b/Assets/Scripts/Zone Display/GasGiantObject.cs
index 81fb45a1d..927513648 100644
--- a/Assets/Scripts/Zone Display/GasGiantObject.cs	
+++ b/Assets/Scripts/Zone Display/GasGiantObject.cs	
@@ -9,5 +9,4 @@ using UnityEngine;
 public class GasGiantObject : PlanetObject
 {
     public SunMaterial SunMaterial;
-    public MeshRenderer GravityWaves;
 }
diff --git a/Assets/Scripts/Zone Display/ZoneRenderer.cs b/Assets/Scripts/Zone Display/ZoneRenderer.cs
index cccb97ebf..907134dbc 100644
--- a/Assets/Scripts/Zone Display/ZoneRenderer.cs	
+++ b/Assets/Scripts/Zone Display/ZoneRenderer.cs	
@@ -27,7 +27,6 @@ public class ZoneRenderer : MonoBehaviour
     public GameSettings Settings;
     public Transform ZoneRoot;
     public Transform SectorBrushes;
-    public MeshRenderer SectorBoundaryBrush;
     public CinemachineVirtualCamera SceneCamera;
     public Camera[] FogCameras;
     public Camera[] MinimapCameras;
@@ -472,17 +471,12 @@ public class ZoneRenderer : MonoBehaviour
                 else planet = Instantiate(GasGiant, ZoneRoot);
 
                 var gas = (GasGiantObject) planet;
-                var gasGiant = Zone.PlanetInstances[key] as GasGiant;
                 gas.Body.material.SetTexture("_ColorRamp", gasGiantData.Colors.ToGradient(!(planetData is SunData)).ToTexture());
                 // gasGiantData.AlbedoRotationSpeed.Subscribe(f => gas.SunMaterial.AlbedoRotationSpeed = f);
                 // gasGiantData.FirstOffsetRotationSpeed.Subscribe(f => gas.SunMaterial.FirstOffsetRotationSpeed = f);
                 // gasGiantData.SecondOffsetRotationSpeed.Subscribe(f => gas.SunMaterial.SecondOffsetRotationSpeed = f);
                 // gasGiantData.FirstOffsetDomainRotationSpeed.Subscribe(f => gas.SunMaterial.FirstOffsetDomainRotationSpeed = f);
                 // gasGiantData.SecondOffsetDomainRotationSpeed.Subscribe(f => gas.SunMaterial.SecondOffsetDomainRotationSpeed = f);
-                gas.GravityWaves.transform.localScale = gasGiant.GravityWavesRadius * Vector3.one;
-                gas.GravityWaves.material.SetFloat("_Depth", gasGiant.GravityWavesDepth);
-                gas.GravityWaves.material.SetFloat("_Frequency", Settings.PlanetSettings.WaveFrequency.Evaluate(planetData.Mass));
-                //gas.WaveScroll.Speed = Properties.GravitySettings.WaveSpeed.Evaluate(f);
             }
             else
             {
@@ -584,8 +578,6 @@ public class ZoneRenderer : MonoBehaviour
             planet.Value.Body.transform.localPosition = new Vector3(0, height + planetInstance.BodyRadius * 2, 0);
             if (planet.Value is GasGiantObject gasGiantObject)
             {
-                gasGiantObject.GravityWaves.material.SetFloat("_Phase",
-                    Zone.Time * ((GasGiant) Zone.PlanetInstances[planet.Key]).GravityWavesSpeed);
                 if (!(planet.Value is SunObject))
                 {
                     var toParent = normalize(Zone.GetOrbitPosition(Zone.Orbits[planetInstance.BodyData.Orbit.Key].Data.Parent.Key) - p);
@@ -618,19 +610,13 @@ public class ZoneRenderer : MonoBehaviour
         }
 
         //var fogPos = FogCameraParent.position;
-        SectorBoundaryBrush.material.SetFloat("_Power", Settings.PlanetSettings.ZoneDepthExponent);
-        SectorBoundaryBrush.material.SetFloat("_Depth", Settings.PlanetSettings.ZoneDepth + Settings.PlanetSettings.ZoneBoundaryFog);
-        var startDepth = Zone.PowerPulse(Settings.MinimapZoneGravityRange, Settings.PlanetSettings.ZoneDepthExponent) *
-                          Settings.PlanetSettings.ZoneDepth;
-        var depthRange = Settings.PlanetSettings.ZoneDepth - startDepth + maxDepth;
+        var depthRange = Mathf.Max(maxDepth, 1f);
         foreach (var mat in MapGravityMaterials)
         {
-            mat.SetFloat("_StartDepth", startDepth);
+            mat.SetFloat("_StartDepth", 0f);
             mat.SetFloat("_DepthRange", depthRange);
         }
-        //Shader.SetGlobalFloat("_GridOffset", Settings.PlanetSettings.ZoneBoundaryFog);
         // var gravPos = MinimapGravityQuad.transform.position;
-        // gravPos.y = -Settings.PlanetSettings.ZoneDepth - _maxDepth;
         // MinimapGravityQuad.transform.position = gravPos;
         // MinimapTintQuad.transform.position = gravPos - Vector3.up*10;
     }
diff --git a/tests/Aetheria.Shared.Tests/EvasionTermTests.cs b/tests/Aetheria.Shared.Tests/EvasionTermTests.cs
index 0b0688457..ffd99d16e 100644
--- a/tests/Aetheria.Shared.Tests/EvasionTermTests.cs
+++ b/tests/Aetheria.Shared.Tests/EvasionTermTests.cs
@@ -81,11 +81,15 @@ public sealed partial class RunStartTests
 
     // Idle long enough for stats and power to reach their idle state, then at rest, facing +y,
     // and, after three seconds of coasting, with nothing observed: the track forgets on its own.
+    // The ship is stepped alone, so the zone's wells pull it while it idles; settling is about stats and power, so
+    // it comes back to where it stood.
     private static void EvSettle(Ship ship)
     {
+        var stood = ship.Position.xz;
         ship.MovementDirection = float2(0, 0);
         EvFace(ship, float3(0, 0, 1));
         for (var step = 0; step < 180; step++) ship.Update(EvDt);
+        ship.Position.xz = stood;
         ship.Velocity = float2(0, 0);
         ship.Direction = float2(0, 1);
     }
diff --git a/tests/Aetheria.Shared.Tests/FireControlTests.cs b/tests/Aetheria.Shared.Tests/FireControlTests.cs
index 24919fba9..d4d0ba50d 100644
--- a/tests/Aetheria.Shared.Tests/FireControlTests.cs
+++ b/tests/Aetheria.Shared.Tests/FireControlTests.cs
@@ -41,7 +41,11 @@ public sealed class FireControlTests : IDisposable
     // A hull with one weapon hardpoint per (rotation, firingArc) pair, laid out along the X axis of a 1xN
     // shape so each gets its own cell. FiringArc 0 on a hardpoint means "use GameplaySettings.FiringArc".
     private (ItemManager items, Ship ship, EquippedItem[] weapons) BuildShipWithHardpoints(
-        params (ItemRotation rotation, float firingArc)[] hardpoints)
+        params (ItemRotation rotation, float firingArc)[] hardpoints) => BuildShipWithHardpoints(false, hardpoints);
+
+    // `well` digs the zone one well at the origin (WellFixture), so heights differ across the zone.
+    private (ItemManager items, Ship ship, EquippedItem[] weapons) BuildShipWithHardpoints(
+        bool well, (ItemRotation rotation, float firingArc)[] hardpoints)
     {
         var hullShape = new Shape(Math.Max(hardpoints.Length, 3), 3);
         foreach (var cell in hullShape.AllCoordinates) hullShape[cell] = true;
@@ -78,13 +82,16 @@ public sealed class FireControlTests : IDisposable
             buildCache.FlushAsync().Wait();
         }
 
-        _openCache = AetheriaStores.Open(Catalog, catalogWritable: true);
+        _openCache = AetheriaStores.Open(Catalog, Path.Combine(_root, "Run.cc"), catalogWritable: true);
         var ledger = new ProvenanceLedger();
         ledger.Lots[1] = new Lot { Origin = new Attributed(), Quality = 1 }; // hull
         for (var i = 0; i < hardpoints.Length; i++)
             ledger.Lots[2 + i] = new Lot { Origin = new Attributed(), Quality = 1 }; // guns
         var items = new ItemManager(_openCache, ledger, TestSettings(), _ => { });
-        var zone = new Zone(items, new PlanetSettings(), new ZonePack(), new GalaxyZone { Name = "Test Zone", Owner = null }, null);
+        var planets = new PlanetSettings();
+        var pack = new ZonePack();
+        if (well) WellFixture.Dig(_openCache, pack, planets, pack.Radius, 1000f, 1f);
+        var zone = new Zone(items, planets, pack, new GalaxyZone { Name = "Test Zone", Owner = null }, null);
 
         var hullRef = items.ItemData.RefOf<ItemData>(items.ItemData.GetByName<HullData>("TestHull"));
         var hull = new EquippableItem { Data = hullRef, Durability = 1, Lot = 1 };
@@ -182,10 +189,10 @@ public sealed class FireControlTests : IDisposable
     }
 
     // A shooter with one in-range, in-arc gun, a detected target at `targetPosition`, and a Minion driving the shooter.
-    private (Ship shooter, Ship target, Zone zone) BuildCombatEncounter(float3 targetPosition, float projectileSpeed = 0f, bool twoTargetGuns = false)
+    private (Ship shooter, Ship target, Zone zone) BuildCombatEncounter(float3 targetPosition, float projectileSpeed = 0f, bool twoTargetGuns = false, bool well = false)
     {
         var mounts = twoTargetGuns ? new[] { (ItemRotation.None, 0f), (ItemRotation.None, 0f) } : new[] { (ItemRotation.None, 0f) };
-        var (items, shooter, weapons) = BuildShipWithHardpoints(mounts);
+        var (items, shooter, weapons) = BuildShipWithHardpoints(well, mounts);
         var weaponData = (InstantWeaponData) weapons[0].Data.Behaviors.Single(b => b is InstantWeaponData);
         weaponData.Damage = new PerformanceStat { Min = 10, Max = 10 };
         weaponData.Cooldown = new PerformanceStat { Min = 1, Max = 1 };
@@ -376,9 +383,7 @@ public sealed class FireControlTests : IDisposable
     [Fact]
     public void TheAIMeasuresTheTargetOnTheGroundPlane()
     {
-        var (shooter, target, zone) = BuildCombatEncounter(float3(0, 0, 600), twoTargetGuns: true);
-        zone.Settings.ZoneDepth = 1000f;
-        zone.Settings.ZoneDepthExponent = 1f;
+        var (shooter, target, zone) = BuildCombatEncounter(float3(0, 0, 600), twoTargetGuns: true, well: true);
         var strong = target.Equipment.Single(x => x.Data.Name == "Gun");
         var weak = target.Equipment.Single(x => x.Data.Name == "WeakGun");
         zone.Update(1f); // heights follow the zone's depth from the first update
diff --git a/tests/Aetheria.Shared.Tests/FloatingBodyTests.cs b/tests/Aetheria.Shared.Tests/FloatingBodyTests.cs
index 5b98ba649..e4ee47cfe 100644
--- a/tests/Aetheria.Shared.Tests/FloatingBodyTests.cs
+++ b/tests/Aetheria.Shared.Tests/FloatingBodyTests.cs
@@ -217,7 +217,7 @@ public sealed class FloatingBodyTests : IDisposable
     // the sign or changing how delta enters the line fails here, not only the Zone function's pin above.
     private Ship ShipAt(float x, out Zone zone)
     {
-        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), catalogWritable: true);
+        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), Path.Combine(_root, Guid.NewGuid().ToString("N") + ".run.cc"), catalogWritable: true);
         _caches.Add(cache);
         var hullShape = new Shape(5, 5);
         foreach (var cell in hullShape.AllCoordinates) hullShape[cell] = true;
@@ -230,8 +230,10 @@ public sealed class FloatingBodyTests : IDisposable
             QualityPriceModifier = new ExponentialLerp()
         };
         var items = new ItemManager(cache, new ProvenanceLedger(), settings, _ => { });
-        var planets = new PlanetSettings { ZoneDepth = 1000, ZoneDepthExponent = 1, GravityStrength = 1 };
-        zone = new Zone(items, planets, new ZonePack { Radius = 1000 }, new GalaxyZone { Name = "Test Zone", Owner = null }, null);
+        var planets = new PlanetSettings { GravityStrength = 1 };
+        var pack = new ZonePack { Radius = 1000 };
+        WellFixture.Dig(cache, pack, planets, 1000, 1000, 1);
+        zone = new Zone(items, planets, pack, new GalaxyZone { Name = "Test Zone", Owner = null }, null);
         var design = cache.GetByName<HullData>("Skiff");
         var hull = new EquippableItem
         {
diff --git a/tests/Aetheria.Shared.Tests/FlowFieldTests.cs b/tests/Aetheria.Shared.Tests/FlowFieldTests.cs
index 2c08c3aa1..4924daa81 100644
--- a/tests/Aetheria.Shared.Tests/FlowFieldTests.cs
+++ b/tests/Aetheria.Shared.Tests/FlowFieldTests.cs
@@ -19,7 +19,7 @@ public sealed class FlowFieldTests : IDisposable
     public FlowFieldTests()
     {
         Directory.CreateDirectory(_root);
-        _cache = AetheriaStores.Open(Path.Combine(_root, "flow.cc"), catalogWritable: true);
+        _cache = AetheriaStores.Open(Path.Combine(_root, "flow.cc"), Path.Combine(_root, "flow-run.cc"), catalogWritable: true);
         _cache.Upsert(new VerseGrammar { Revision = 1 });
         _cache.FlushAsync().Wait();
         var settings = new GameplaySettings
@@ -46,9 +46,13 @@ public sealed class FlowFieldTests : IDisposable
     };
 
     // A zone at `time` (the pack's clock, as a saved zone restores it), flat unless `depth` digs the zone's own well.
-    private Zone ZoneWith(FlowSettings flow, double time = 0, float depth = 0f) => new Zone(_items,
-        new PlanetSettings { Flow = flow, ZoneDepth = depth, ZoneDepthExponent = 2f },
-        new ZonePack { Time = time }, new GalaxyZone { Name = "Flow Zone", Owner = null }, null);
+    private Zone ZoneWith(FlowSettings flow, double time = 0, float depth = 0f)
+    {
+        var planets = new PlanetSettings { Flow = flow };
+        var pack = new ZonePack { Time = time };
+        if (depth > 0f) WellFixture.Dig(_items.ItemData, pack, planets, pack.Radius, depth, 2f);
+        return new Zone(_items, planets, pack, new GalaxyZone { Name = "Flow Zone", Owner = null }, null);
+    }
 
     private static readonly float3[] Probes =
     {
diff --git a/tests/Aetheria.Shared.Tests/GravitySubtractTests.cs b/tests/Aetheria.Shared.Tests/GravitySubtractTests.cs
new file mode 100644
index 000000000..7f89cd0fd
--- /dev/null
+++ b/tests/Aetheria.Shared.Tests/GravitySubtractTests.cs
@@ -0,0 +1,164 @@
+using System;
+using System.IO;
+using CultMath;
+using GameCult.Caching;
+using Xunit;
+using float2 = CultMath.float2;
+using float3 = CultMath.float3;
+
+// flatspace-no-bowl-no-ripples (aetheria-gravity target r3): a zone's height is the sum of its bodies' wells and
+// nothing else. No zone-wide bowl sized by the pack, and no gas-giant or sun ripple that varies with zone time.
+public sealed class GravitySubtractTests : IDisposable
+{
+    private readonly string _root = Path.Combine(Path.GetTempPath(), "aetheria-gravsub-" + Guid.NewGuid().ToString("N"));
+    private readonly CultCache _cache;
+    private readonly ItemManager _items;
+
+    public GravitySubtractTests()
+    {
+        Directory.CreateDirectory(_root);
+        _cache = AetheriaStores.Open(Path.Combine(_root, "grav.cc"), Path.Combine(_root, "grav-run.cc"), catalogWritable: true);
+        _cache.Upsert(new VerseGrammar { Revision = 1 });
+        _cache.FlushAsync().Wait();
+        var settings = new GameplaySettings
+        {
+            DefaultEntitySettings = new EntitySettings(),
+            Tiers = new[] { new RarityTier { Name = "Common", Quality = .5f, Rarity = 0, Color = new float3(1, 1, 1) } },
+            QualityPriceModifier = new ExponentialLerp(),
+            TargetDetectionInfoThreshold = .1f, TargetGearInfoThreshold = .8f,
+            FiringArc = 170, CommitHorizon = .5f, SchematicCellSize = 2f
+        };
+        _items = new ItemManager(_cache, new ProvenanceLedger(), settings, _ => { });
+    }
+
+    public void Dispose()
+    {
+        _cache.Dispose();
+        Directory.Delete(_root, true);
+    }
+
+    // Curves for a body whose well, light and orbit all vary with mass, so a body that read a different
+    // mass or multiplier than its twin would show it.
+    private static PlanetSettings Planets() => new PlanetSettings
+    {
+        GravityStrength = 1,
+        BodyRadius = new ExponentialCurve { Exponent = .25f, Multiplier = 3f },
+        GravityRadius = new ExponentialCurve { Exponent = .25f, Multiplier = 500f },
+        GravityDepth = new ExponentialCurve { Exponent = .175f, Multiplier = 30f },
+        LightRadius = new ExponentialCurve { Exponent = .25f, Multiplier = 300f },
+        OrbitPeriod = new ExponentialCurve()
+    };
+
+    private Zone Bare(float packRadius) => new Zone(_items, Planets(), new ZonePack { Radius = packRadius },
+        new GalaxyZone { Name = "Bare Zone", Owner = null }, null);
+
+    [Fact]
+    public void AZoneWithNoBodiesIsFlat()
+    {
+        foreach (var packRadius in new[] { 1000f, 2500f })
+        {
+            var zone = Bare(packRadius);
+            foreach (var r in new[] { 0f, 300f, 577f, 900f, 2000f })
+            {
+                var at = new float2(r, 0);
+                Assert.Equal(0f, zone.GetHeight(at));
+                Assert.Equal(0f, zone.GetForce(at).x);
+                Assert.Equal(0f, zone.GetForce(at).y);
+                var inPlane = new float2(0, r);
+                Assert.Equal(0f, zone.GetHeight(inPlane));
+                Assert.Equal(0f, zone.GetForce(inPlane).x);
+                Assert.Equal(0f, zone.GetForce(inPlane).y);
+            }
+        }
+    }
+
+    // The fixture the five bowl tests share reproduces the zone bowl it replaced (map B14): the bowl was
+    // -PowerPulse(r / (2 R), exponent) x depth, written out here from its definition, deepest at the centre and
+    // zero from r = R on, so a fixture whose radius or depth drifted from the bowl would change every pull it feeds.
+    [Fact]
+    public void TheWellFixtureReproducesTheFormerBowl()
+    {
+        foreach (var (radius, depth, exponent, at, expected) in new[]
+                 {
+                     (1000f, 1000f, 1f, 0f, -1000f), (1000f, 1000f, 1f, 400f, -840f), (1000f, 1000f, 1f, 1000f, 0f),
+                     (2000f, 64f, 2f, 1000f, -36f), (2000f, 64f, 2f, 300f, -61.1524f)
+                 })
+        {
+            var planets = Planets();
+            var pack = new ZonePack { Radius = radius };
+            WellFixture.Dig(_cache, pack, planets, radius, depth, exponent);
+            var zone = new Zone(_items, planets, pack, new GalaxyZone { Name = "Bowl Zone", Owner = null }, null);
+            Assert.InRange(zone.GetHeight(new float2(at, 0)), expected - 1e-2f, expected + 1e-2f);
+        }
+    }
+
+    // One body of `data` at the origin of a zone whose only body it is.
+    private Zone WithBody(BodyData data)
+    {
+        var orbit = _cache.Upsert(new OrbitData { FixedPosition = float2.zero }).Key;
+        data.Orbit = new CultRecordRef<OrbitData>(orbit);
+        data.Mass = 100f;
+        data.GravityRadiusMultiplier = 1.5f;
+        data.GravityDepthMultiplier = .7f;
+        data.GravityDepthExponent = 2f;
+        var body = _cache.Upsert(data).Key;
+        var pack = new ZonePack { Radius = 1000f };
+        pack.Orbits.Add(new CultRecordRef<OrbitData>(orbit));
+        pack.Planets.Add(new CultRecordRef<BodyData>(body));
+        return new Zone(_items, Planets(), pack, new GalaxyZone { Name = "Giant " + data.GetType().Name, Owner = null }, null);
+    }
+
+    // The wells are the whole of a giant's height at every point, not just at a few radii: a ripple confined to
+    // any annulus, or to a band derived from the body's radius, shows against the plain body somewhere in a sweep
+    // that runs from the centre to well past the well's support.
+    [Fact]
+    public void AGiantsWellIsAPlainWellAtEveryTime()
+    {
+        var plain = WithBody(new PlanetData());
+        var giants = new[] { WithBody(new GasGiantData()), WithBody(new SunData()) };
+        var radii = new System.Collections.Generic.List<float> { 0.5f };
+        for (var r = 1f; r <= 100f; r += 1f) radii.Add(r);
+        for (var r = 105f; r <= 2000f; r += 5f) radii.Add(r);
+        var angles = new[] { 0f, 0.7f, 2.1f, 4.0f };
+        foreach (var time in new[] { 0f, 37.5f, 91.25f })
+        {
+            // Zone time 0 is the zones as built; each later time is one Update to that time.
+            var step = time - _clock;
+            if (step > 0f)
+            {
+                plain.Update(step);
+                foreach (var giant in giants) giant.Update(step);
+                _clock = time;
+            }
+            foreach (var r in radii)
+            foreach (var a in angles)
+            {
+                var at = new float2(r * (float)Math.Cos(a), r * (float)Math.Sin(a));
+                foreach (var giant in giants)
+                {
+                    Assert.Equal(plain.GetHeight(at), giant.GetHeight(at));
+                    Assert.Equal(plain.GetForce(at).x, giant.GetForce(at).x);
+                    Assert.Equal(plain.GetForce(at).y, giant.GetForce(at).y);
+                }
+            }
+            Assert.True(plain.GetHeight(new float2(50f, 0)) < 0f, "the plain body digs a well here, so there is something to compare");
+        }
+    }
+
+    private float _clock;
+
+    // CultCache has no primitive for reserving a removed MessagePack key; the wave keys of the gas giant (14-17)
+    // must not come back with a different meaning, because stored records may still carry them.
+    [Fact]
+    public void AGasGiantRecordNeverReusesTheRetiredWaveKeys()
+    {
+        var keys = new System.Collections.Generic.List<int>();
+        for (var t = typeof(GasGiantData); t != null; t = t.BaseType)
+            foreach (var m in t.GetMembers(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic |
+                                           System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.DeclaredOnly))
+                if (m.GetCustomAttributes(typeof(MessagePack.KeyAttribute), false) is MessagePack.KeyAttribute[] ks)
+                    foreach (var k in ks) if (k.IntKey.HasValue) keys.Add(k.IntKey.Value);
+        Assert.NotEmpty(keys);
+        foreach (var retired in new[] { 14, 15, 16, 17 }) Assert.DoesNotContain(retired, keys);
+    }
+}
diff --git a/tests/Aetheria.Shared.Tests/LootTests.cs b/tests/Aetheria.Shared.Tests/LootTests.cs
index 6b736fa23..5a5bfce7d 100644
--- a/tests/Aetheria.Shared.Tests/LootTests.cs
+++ b/tests/Aetheria.Shared.Tests/LootTests.cs
@@ -61,7 +61,7 @@ public sealed class LootTests : IDisposable
     }
 
     private Lab Build(string zoneName = "Loot", float probability = .5f, float lifetime = 30f, float velocity = 25f,
-        PlanetSettings planets = null, float spread = 0f)
+        bool well = false, float spread = 0f)
     {
         var settings = new GameplaySettings
         {
@@ -73,7 +73,7 @@ public sealed class LootTests : IDisposable
             UnaidedAccuracy = .05f, UnaidedTracking = 10f, UnaidedPrecision = 2f, AgentMinHitProbability = 0f,
             LootDropProbability = probability, LootDropVelocity = velocity, FloatingItemLifetime = lifetime
         };
-        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), catalogWritable: true);
+        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), Path.Combine(_root, Guid.NewGuid().ToString("N") + ".run.cc"), catalogWritable: true);
         _caches.Add(cache);
         cache.Upsert(new VerseGrammar { Revision = 1 });
         var hardpoint = new HardpointData { Type = HardpointType.Sensors, Position = new int2(0, 0), Shape = new Shape() };
@@ -108,7 +108,14 @@ public sealed class LootTests : IDisposable
         var ledger = new ProvenanceLedger();
         for (var i = 1; i <= 9000; i++) ledger.Lots[i] = new Lot { Origin = new Attributed(), Quality = 1 };
         var items = new ItemManager(cache, ledger, settings, _ => { });
-        var zone = new Zone(items, planets ?? new PlanetSettings(), new ZonePack { Radius = planets == null ? 0 : 1000 }, new GalaxyZone { Name = zoneName, Owner = null }, null);
+        var planets = new PlanetSettings();
+        var pack = new ZonePack { Radius = well ? 1000 : 0 };
+        if (well)
+        {
+            planets.GravityStrength = 1;
+            WellFixture.Dig(cache, pack, planets, 1000, 1000, 1);
+        }
+        var zone = new Zone(items, planets, pack, new GalaxyZone { Name = zoneName, Owner = null }, null);
         return new Lab { Items = items, Zone = zone };
     }
 
@@ -286,8 +293,7 @@ public sealed class LootTests : IDisposable
     [Fact]
     public void AFloatingItemDriftsAsABodyAndExpires()
     {
-        var planets = new PlanetSettings { ZoneDepth = 1000, ZoneDepthExponent = 1, GravityStrength = 1 };
-        var lab = Build(lifetime: 3f, planets: planets);
+        var lab = Build(lifetime: 3f, well: true);
         var settings = lab.Items.GameplaySettings;
         var start = new float2(40, -25);
         var launch = new float2(6, 2);
diff --git a/tests/Aetheria.Shared.Tests/MineTests.cs b/tests/Aetheria.Shared.Tests/MineTests.cs
index c997041a4..4d42e0add 100644
--- a/tests/Aetheria.Shared.Tests/MineTests.cs
+++ b/tests/Aetheria.Shared.Tests/MineTests.cs
@@ -78,7 +78,7 @@ public sealed class MineTests : IDisposable
             FiringArc = 170, CommitHorizon = .5f, SchematicCellSize = 2f,
             UnaidedAccuracy = .05f, UnaidedTracking = 10f, UnaidedPrecision = 1000f, AgentMinHitProbability = 0f
         };
-        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), catalogWritable: true);
+        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), Path.Combine(_root, Guid.NewGuid().ToString("N") + ".run.cc"), catalogWritable: true);
         _caches.Add(cache);
         cache.Upsert(new VerseGrammar { Revision = 1 });
         HullData Hull(string name, Shape shape) => new HullData
@@ -118,8 +118,10 @@ public sealed class MineTests : IDisposable
         var ledger = new ProvenanceLedger();
         for (var i = 1; i <= 500; i++) ledger.Lots[i] = new Lot { Origin = new Attributed(), Quality = 1 };
         var items = new ItemManager(cache, ledger, settings, _ => { });
-        var planets = well ? new PlanetSettings { ZoneDepth = 1000, ZoneDepthExponent = 1, GravityStrength = 1 } : new PlanetSettings();
-        var zone = new Zone(items, planets, new ZonePack { Radius = well ? 1000 : 0 }, new GalaxyZone { Name = "Mines", Owner = null }, null);
+        var planets = well ? new PlanetSettings { GravityStrength = 1 } : new PlanetSettings();
+        var pack = new ZonePack { Radius = well ? 1000 : 0 };
+        if (well) WellFixture.Dig(cache, pack, planets, 1000, 1000, 1);
+        var zone = new Zone(items, planets, pack, new GalaxyZone { Name = "Mines", Owner = null }, null);
         var lab = new Lab { Items = items, Zone = zone, Data = data, ItemData = cache.GetByName<WeaponItemData>("Mine Layer") };
 
         var layerRef = items.ItemData.RefOf<ItemData>(items.ItemData.GetByName<HullData>("Layer"));
diff --git a/tests/Aetheria.Shared.Tests/MiningCut3Tests.cs b/tests/Aetheria.Shared.Tests/MiningCut3Tests.cs
index 8ad9d8fc3..273b63547 100644
--- a/tests/Aetheria.Shared.Tests/MiningCut3Tests.cs
+++ b/tests/Aetheria.Shared.Tests/MiningCut3Tests.cs
@@ -58,10 +58,6 @@ public sealed partial class MiningCut3Tests : IDisposable
         BodyRadius = new ExponentialCurve(),
         GravityRadius = new ExponentialCurve(),
         GravityDepth = new ExponentialCurve(),
-        WaveDepth = new ExponentialCurve(),
-        WaveRadius = new ExponentialCurve(),
-        WaveSpeed = new ExponentialCurve(),
-        WaveFrequency = new ExponentialCurve(),
         LightRadius = new ExponentialCurve { Constant = lightRadius }
     };
 
diff --git a/tests/Aetheria.Shared.Tests/WellFixture.cs b/tests/Aetheria.Shared.Tests/WellFixture.cs
new file mode 100644
index 000000000..ab6922cd7
--- /dev/null
+++ b/tests/Aetheria.Shared.Tests/WellFixture.cs
@@ -0,0 +1,21 @@
+using CultMath;
+using GameCult.Caching;
+
+// The one fixture that gives a test zone a slope: a single body on a parentless orbit at the origin, with
+// the curves a body needs. Gravity height is the sum of body wells, so a test that wants ground to slide on
+// digs it here and nowhere else. `radius` is the zone radius the well is sized to (its well reaches 2 x radius,
+// as the former bowl did); the well is deepest at the centre and zero at and beyond half its radius.
+internal static class WellFixture
+{
+    public static void Dig(CultCache cache, ZonePack pack, PlanetSettings settings, float radius, float depth, float exponent)
+    {
+        settings.BodyRadius = new ExponentialCurve();
+        settings.OrbitPeriod = new ExponentialCurve();
+        settings.GravityRadius = new ExponentialCurve { Constant = 2f * radius };
+        settings.GravityDepth = new ExponentialCurve { Constant = depth };
+        var orbit = cache.Upsert(new OrbitData { FixedPosition = float2.zero }).Key;
+        var body = cache.Upsert(new PlanetData { Orbit = new CultRecordRef<OrbitData>(orbit), GravityDepthExponent = exponent }).Key;
+        pack.Orbits.Add(new CultRecordRef<OrbitData>(orbit));
+        pack.Planets.Add(new CultRecordRef<BodyData>(body));
+    }
+}
diff --git a/tests/Aetheria.Shared.Tests/ZonePlacedAtBuildTests.cs b/tests/Aetheria.Shared.Tests/ZonePlacedAtBuildTests.cs
new file mode 100644
index 000000000..002f0f2df
--- /dev/null
+++ b/tests/Aetheria.Shared.Tests/ZonePlacedAtBuildTests.cs
@@ -0,0 +1,161 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using CultMath;
+using GameCult.Caching;
+using Xunit;
+using static CultMath.math;
+using float2 = CultMath.float2;
+using float3 = CultMath.float3;
+
+// Aetheria gravity, target invariant zone-valid-before-tick: a zone's orbits are placed when it is built, so
+// its wells, lights and body poses are right before the first Update (follow-up
+// aetheria-release:follow_up:zone-orbits-unplaced-before-first-tick). The zone here is the production
+// constructor reading a pack; nothing places an orbit but that constructor and Zone.Update.
+public sealed class ZonePlacedAtBuildTests : IDisposable
+{
+    private static readonly float2 RootAt = new float2(300f, -200f);
+    private const float Distance = 400f;
+    private const float Period = 40f;
+
+    private readonly string _root = Path.Combine(Path.GetTempPath(), "aetheria-zoneplaced-" + Guid.NewGuid().ToString("N"));
+    private readonly List<CultCache> _caches = new List<CultCache>();
+
+    public ZonePlacedAtBuildTests() => Directory.CreateDirectory(_root);
+
+    public void Dispose()
+    {
+        foreach (var cache in _caches) cache.Dispose();
+        Directory.Delete(_root, true);
+    }
+
+    private static GameplaySettings GameSettings() => new GameplaySettings
+    {
+        DefaultEntitySettings = new EntitySettings(),
+        Tiers = new[] { new RarityTier { Name = "Common", Quality = .5f, Rarity = 0, Color = new float3(1, 1, 1) } },
+        QualityPriceModifier = new ExponentialLerp()
+    };
+
+    private static ExponentialCurve Flat(float v) => new ExponentialCurve { Constant = v };
+
+    // Flat space (no zone depth) with one planet whose well reaches 500 u, a fixed root orbit at RootAt and the
+    // planet orbiting it at Distance from `phase`. Every orbit period is Period seconds.
+    private static PlanetSettings Settings() => new PlanetSettings
+    {
+        OrbitPeriod = Flat(Period),
+        BodyRadius = Flat(20f),
+        GravityRadius = Flat(500f),
+        GravityDepth = Flat(100f),
+        GravityStrength = 1f,
+        LightRadius = Flat(0f)
+    };
+
+    private sealed class Scene
+    {
+        public CultCache Cache;
+        public ItemManager Items;
+        public HullData Hull;
+        public Zone Zone;
+        public CultRecordKey PlanetOrbit;
+    }
+
+    private Scene Build(float phase, double time, bool moonFirst = false)
+    {
+        var dir = Path.Combine(_root, $"zone{_caches.Count}");
+        Directory.CreateDirectory(dir);
+        var cache = AetheriaStores.Open(Path.Combine(dir, "Aetheria.cc"), Path.Combine(dir, "run.cc"), catalogWritable: true);
+        _caches.Add(cache);
+        cache.Upsert(new VerseGrammar { Revision = 1 });
+        var shape = new Shape(5, 5);
+        foreach (var cell in shape.AllCoordinates) shape[cell] = true;
+        var hull = new HullData { Name = "Skiff", HullType = HullType.Ship, Shape = shape, Durability = 10, Mass = 1000 };
+        cache.Upsert(hull);
+        var items = new ItemManager(cache, new ProvenanceLedger(), GameSettings(), _ => { });
+
+        var rootOrbit = cache.Upsert(new OrbitData { FixedPosition = RootAt }).Key;
+        var planetOrbit = cache.Upsert(new OrbitData
+        {
+            Parent = new CultRecordRef<OrbitData>(rootOrbit), Distance = Distance, Phase = phase
+        }).Key;
+        var moonOrbit = cache.Upsert(new OrbitData
+        {
+            Parent = new CultRecordRef<OrbitData>(planetOrbit), Distance = 100f
+        }).Key;
+        var planet = cache.Upsert(new PlanetData { Orbit = new CultRecordRef<OrbitData>(planetOrbit), Mass = 1f }).Key;
+        var pack = new ZonePack
+        {
+            Planets = { new CultRecordRef<BodyData>(planet) },
+            Radius = 5000f,
+            Mass = 10000f,
+            Time = time
+        };
+        // The same three orbits either way; only the order the pack lists them in differs.
+        var listed = moonFirst ? new[] { moonOrbit, planetOrbit, rootOrbit } : new[] { rootOrbit, planetOrbit, moonOrbit };
+        foreach (var key in listed) pack.Orbits.Add(new CultRecordRef<OrbitData>(key));
+        var zone = new Zone(items, Settings(), pack, new GalaxyZone { Name = "Placed", Owner = null }, null);
+        return new Scene { Cache = cache, Items = items, Hull = hull, Zone = zone, PlanetOrbit = planetOrbit };
+    }
+
+    [Theory]
+    [InlineData(.1f, 0.0)]
+    [InlineData(.35f, 0.0)]
+    [InlineData(.1f, 123.0)]
+    [InlineData(.35f, 123.0)]
+    public void ABodysWellSitsOnItsOrbitBeforeTheFirstTick(float phase, double time)
+    {
+        var s = Build(phase, time);
+        var orbit = s.Zone.Orbits[s.PlanetOrbit];
+        var turns = (float) frac(time / orbit.Period);
+        var expected = RootAt + OrbitData.Evaluate(frac(turns + phase)) * Distance;
+
+        Assert.InRange(length(orbit.Position - expected), 0f, .01f);
+
+        // The well pulls toward the body's place: a point 30 u east of it is pushed west.
+        var force = s.Zone.GetForce(expected + new float2(30f, 0f));
+        Assert.True(length(force) > 0f, "the well exerts a force");
+        Assert.InRange(normalize(force).x, -1f, -.99f);
+    }
+
+    // A parent's velocity is its own orbital velocity on the first tick and every tick after, whichever order
+    // the pack lists a moon and its planet in. dt differs per tick so a velocity taken from a fixed step fails.
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void TheFirstTickVelocityIsTheOrbitsSpeed(bool moonFirst)
+    {
+        var s = Build(.35f, 0.0, moonFirst);
+        var expected = 2f * PI * Distance / Period;
+        foreach (var dt in new[] { 1f / 60f, 1f / 30f, 1f / 60f })
+        {
+            s.Zone.Update(dt);
+            var speed = length(s.Zone.Orbits[s.PlanetOrbit].Velocity);
+            Assert.InRange(speed, expected * .99f, expected * 1.01f);
+        }
+    }
+
+    [Fact]
+    public void AShipSteppedAloneFeelsTheBodyWhereItIs()
+    {
+        var s = Build(.1f, 0.0);
+        var planetAt = s.Zone.Orbits[s.PlanetOrbit].Position;
+        var ship = new Ship(s.Items, s.Zone, new EquippableItem
+        {
+            Data = s.Cache.RefOf<ItemData>(s.Hull),
+            Durability = s.Hull.Durability,
+            Lot = s.Items.Lots.Add(new Lot
+            {
+                Design = s.Cache.RefOf<ItemData>(s.Hull), Origin = new Attributed(), Quality = .5f, Roles = new List<RoleFill>()
+            })
+        }, new EntitySettings());
+        s.Zone.Admit(ship, piloted: false);
+        var at = planetAt + new float2(0f, 60f);
+        ship.Position = float3(at.x, ship.Position.y, at.y);
+        ship.Velocity = float2.zero;
+
+        ship.Update(1f / 60f); // the ship alone: no Zone.Update has run
+
+        Assert.True(length(ship.Velocity) > 0f, "the ship is pulled");
+        var toward = normalize(planetAt - at);
+        Assert.True(dot(normalize(ship.Velocity), toward) > .99f, "the pull is toward the planet, not toward the origin");
+    }
+}