A Macro-Mechanical Structural Model for Contact Binary Mergers: Shell Compliance and Vent-Induced Interlocking in (486958) Arrokoth

(486958) Arrokoth is the most primitive solar system object yet directly observed, a contact binary formed by the gentle sub-catastrophic merger of two lobes — Wenu and Weeyo — in the primordial Kuiper Belt at an estimated collision velocity of 2 to 5 m/s. The survival of both lobes through this merger, given that cryogenic water ice at 40 K behaves mechanically as a granite-equivalent brittle solid, poses a structural mechanics problem that existing grain-scale particle simulation models (Discrete Element Modeling) address through statistical energy distribution but do not resolve through geometric analysis. This paper introduces two complementary engineering frameworks absent from the existing literature. First, we propose a Structural Shell Compliance model in which the flattened, oblate geometry of each lobe functions as a thin-walled shell — a classical structural topology known to distribute impact stress across an entire curved surface rather than concentrating it at the contact point, enabling brittle materials to survive collisions that a solid body of equivalent composition could not. Second, we introduce the concept of Vent-Induced Interlocking — a mechanism in which internal outgassing occurring while two surfaces are in high-friction contact creates localised surface deformations at regular intervals that act as passive mechanical fasteners, securing the binary joint against subsequent torque and separation forces. We argue that the regular, aligned pit-chain morphology observed at the neck region of Arrokoth is consistent with, and may constitute physical evidence for, this interlocking mechanism. Together these frameworks provide a first-principles macro-structural engineering explanation for the formation and structural integrity of primordial contact binaries.