Physical Characterization of Moon Impactor WE0913A

On March 4, 2022, the object provisionally known as WE0913A crashed into the Moon after several close flybys of the Earth and the Moon in the previous three months. Leading up to impact, the true identity of the lunar-impactor was up for debate with two possibilities: the Falcon 9 rocket from the DSCOVR mission or the Long March 3C from the Chang’e 5-T1 mission. In this paper, we present a trajectory and spectroscopic analysis using ground-based telescope observations to show conclusively that WE0913A is the Long March 3C R/B from the Chang’e 5-T1 mission. Analysis of photometric light curves collected before impact give a spin period of 185.221 ± 6.540 s at a 1σ confidence level just before the first close Earth fly-by on January 20, 2022, and a period of 177.754 ± 0.779 s at a 1σ confidence level just before the second close Earth fly-by on February 8, 2022. Using Markov Chain Monte Carlo sampling and a predictive light curve simulation based on an anisotropic Phong reflection model, we estimate both physical and dynamical properties of the Chang’e 5-T1 rocket body at the start of an observation epoch. The results from the Bayesian analysis imply that there may have been additional mass on the front of the rocket body. Using our predicted impact location on the lunar surface, the Lunar Reconnaissance Orbiter was able to find and image the crater site approximately 7.5 km from prediction. Comparing the pre- and post-impact images of the location shows two distinct craters side-by-side that were made by the Chang’e 5-T1 R/B. The double crater supports the hypothesis that there was possibly an additional mass at the front of the rocket body.