From flash to crater: morphological and spectral analysis of the brightest lunar impact on 2013 September 11 using <i>LRO</i> data

Abstract We present a comprehensive morphological and spectrophotometric analysis of the lunar impact that occurred on 2013 September 11, based on pre- and post-event observations by the Lunar Reconnaissance Orbiter (LRO). The crater formed exhibits a rim-to-rim diameter of 35 ± 0.7 m, a depth of 4.9 ± 0.4 m, and an ejecta blanket extending over 2 km with an area of approximately 7 × 10⁵ m². The ejecta shows a pronounced asymmetry and, assuming uniform distribution, an average thickness limit of ∼2 mm. Spectral analysis using Wide-Angle Camera (WAC) images reveals a consistent reddening of the central ejecta region, with an average 16.54 per cent increase in spectral slope between 321 and 643 nm, marking the first reported detection of colour changes resulting from a lunar impact. We evaluated several scaling laws and found that the Gault formulation most accurately reproduces the observed crater size. Furthermore, luminous efficiency values below η = 2 × 10⁻³ and higher projectile densities are most consistent with the morphology of the ejecta. The impact direction inferred from this pattern is not compatible with the radiant of the September ε-Perseids stream. Moreover, an independent probability analysis yields a greater than 96 per cent likelihood that the event was caused by a sporadic meteoroid. Our results also demonstrate the potential of WAC imagery for the automated detection of new lunar craters, which can improve statistical estimates of the current impact flux. This methodology offers a powerful complement to high-resolution imaging, with important implications for both lunar safety and planetary defense.