Aetheria/docs/aetheria-gravity-target.md

Aetheria gravity: target

Campaign aetheria-gravity. Opened 2026-10-14 on operator ruling aetheria-release:ruling:gravity-honest-wells-agreed. Its invariants, not-in-scope list and canonical implementations are the typed target aetheria-gravity:target:r1; this page keeps the rationale.

Why

The orbit probe (docs/research/2026-10-13-orbit-probe/report.md) measured today's wells against the real code:

• The heightfield is not a potential. Each well is a positive core plus an equal negative-density ring (antimass) out to its rim, so it is mass-neutral and nothing is felt outside the rim.
• The force is S*R*|grad h|^2 behind a slope gate (|n_xz|^2 > 0.001), which zeroes it in every core, at every rim, and in every zone bowl wider than about 3117 units.
• The outer half of every well has unstable circular orbits, and about 40% of moons sit there.
• The wells pull 20 to 70 times harder than the OrbitPeriod rail implies, so holding a rail orbit costs a real fraction of a ship's thrust.

The operator's frame (2026-10-13): bodies sit above the grid so there is always room to fly beneath them, so being within a sun's radius is not being inside it; gravity is shaped that way on purpose, and the picture is why it looks as it does. "We can use correct wells and simply exaggerate the height."

The shape

One scalar potential per zone owns gravity. Each body contributes a 2D point-mass well: logarithmic potential and force falling as 1/r outside the body's radius, softened inside it (force linear to zero at the centre, matched in value and slope at the radius, Plummer-like). Wells add. Force is the potential's gradient, with no gate. The drawn height is the potential times one exaggeration factor, so what the player sees and what the ship feels are the same function. With a 1/r tail every circular orbit is stable.

In Ink zones the Adrasteia pillars stand where suns would (aetheria-fauna:ruling:ink-pillars-are-suns): a pillar is the zone's central body, and by this campaign its well follows the same law.

What the first Imagination pass settles (step 0b)

• Whether the rails (OrbitPeriod) are derived from the field, or the field is calibrated to the rails. Today they disagree by 20-70x in force; one must own the other.
• What becomes of the zone bowl and of the gas-giant and sun waves: parts of the potential, a separate push, or gone.
• Hull drag and real ship acceleration (unmeasured by the probe), which decide whether a free orbit is possible and how much lighter near-body flight feels.
• Every reader of Zone.GetHeight, GetForce and GravityAcceleration (sim, AI, renderer, shaders), so the potential has one owner and the height is derived from it everywhere.
• Follow-up aetheria-release:follow_up:zone-orbits-unplaced-before-first-tick: a zone must be valid before its first tick, or every well sits at the origin.

Not here

Portals and portal gravity, and non-Euclidean zone geometry, belong to the pseudospace-flavours line (aetheria-release:follow_up:portals-and-portal-gravity, aetheria-release:follow_up:pseudospace-geometry-owner).