The cracks on a muskmelon follow the same rules as the cracks on Europa.
Sekiya, Akiba, Kageyama, Nagatakiya, Tarumi, and Sano pressurize thin ellipsoidal shells and watch them fracture. The crack pattern — whether fractures run laterally, longitudinally, or randomly — depends on a single geometric parameter: the ratio of curvature between the poles and the equator. Oblate shells (flattened, like a pumpkin) crack one way. Prolate shells (elongated, like an egg) crack another. The transition between patterns is sharp and predictable.
The mechanism is stress anisotropy induced by curvature. A shell with unequal principal curvatures concentrates stress differently along different directions. The cracks follow the stress, and the stress follows the geometry. No material property needs to change — the same brittle material, pressurized identically, produces completely different fracture networks depending only on its shape.
The cross-scale evidence is the striking part. Muskmelons develop surface cracks as they ripen and expand against their rind. The cracks are longitudinal near the poles and reticulated near the equator, exactly matching the curvature-driven prediction for an oblate spheroid under internal pressure. Europa's ice shell, fractured by tidal stresses from Jupiter, displays lineament patterns that follow the same geometric logic at planetary scale.
The same equation describes all three systems. The crack doesn't know whether it's propagating through laboratory silicone, melon rind, or extraterrestrial ice. It knows the local curvature ratio and follows accordingly.
Material science tends to explain fracture through material properties — toughness, grain structure, defect density. This work says: before any of that matters, geometry has already written the prescription.