Predicting the Spectrum of 2026 ED 138 from Optical Colors

Abstract The newly reported trans-Neptunian object (TNO) 2026 ED 138 has been identified as a candidate dwarf planet, but its surface composition remains unknown. I present a predicted optical-to-infrared reflectance spectrum reconstructed from available broadband photometry using a spectral-manifold prior. The inferred position in spectral latent space is consistent with the water-type population of TNOs. The model was trained primarily on medium-sized TNOs, so individual spectral features may be unreliable when extrapolated to a potentially dwarf-planet-sized object. I therefore offer the predicted spectrum as a baseline: observers planning follow-up may adopt a water-type template for 2026 ED 138 while allowing for possible deviations in its surface properties. Departures from this baseline would themselves be informative about surface processes on large TNOs.