The Photonic Universe Hypothesis (PUH) makes the entrenched postulate , established across Theorem 140 (complete amalgamation), Theorem 196 (skeleton solar system from momentum sorting), and Theorem 197 (Planck core as universal internal heat source), that every gravitationally bound object contains a primordial Planck core inherited from the Z₃-asymmetric rebound. For Earth specifically, this claim predicts that some fraction of the planet’s internal heat output originates not from radiogenic decay or secular cooling but from Casimir-constraint heat flux at the central Planck Shell (T197). This Lead Note proposes a quantitative test of that prediction using existing geoneutrino measurements. Earth’s total surface heat flux is approximately 47 TW (Davies and Davies 2010 consensus). KamLAND (2005-present) and Borexino (2007-present) have directly measured the geoneutrino flux from U-238 and Th-232 decay chains in Earth’s interior, giving a combined radiogenic heat estimate of approximately 20 TW (with substantial uncertainty, roughly 12 to 28 TW depending on Bulk Silicate Earth model assumptions). K-40 antineutrinos lie below current detector thresholds and contribute an additional approximately 4 TW estimated from cosmochemical modeling. The total radiogenic heat is therefore approximately 24 TW, leaving approximately 23 TW of non-radiogenic heat unaccounted for by direct measurement. Mainstream geophysics attributes this 23 TW remainder to secular cooling and latent heat fro