The canonical giant impact hypothesis requires the impactor Theia to have formed at the same heliocentric distance as Earth to reproduce the observed oxygen and chromium isotopic identity between Earth and Moon — an unsubstantiated coincidence. This paper proposes that the Moon formed from a large mantle fragment of Tiamat, a ~0.5 M⊕ differentiated embryo that accreted at 2-3 au and was tidally disrupted by Jupiter during the Grand Tack migration. N-body simulations (>5000 test particles, 13 configurations) show that Earth-crossing efficiency depends on Jupiter's position: 0.58% at 5.2 au, rising 60-fold to 31.25% at 2.0 au with Saturn. Angular momentum analysis of 466 Earth-crossing fragments yields a predicted obliquity of 0.77°, far below Earth's 23.44°, requiring a final large impactor — Theia — whose isotopic identity with Earth is guaranteed by their common origin from the same disruption event. The model simultaneously explains nine independent observations: (1) iron depletion; (2) oxygen isotopic identity; (3) chromium isotopic identity; (4) volatile depletion; (5) Galilean satellites; (6) Venus' rotation; (7) Jupiter's heavy element enrichment; (8) asteroid belt origin; and (9) Theia's origin as a derived consequence. The Fe₃P-bearing fragments also delivered activated phosphorus relevant to prebiotic chemistry and the timing of complex life emergence. Six falsifiable predictions are presented for Europa Clipper, JUICE, and future missions.
FatJack (Thu,) studied this question.