Abstract: "The near-Earth asteroid 2024 YR4 -- a ∼60 m rocky object that was once considered a potential Earth impactor -- has since been ruled out for Earth but retained a ∼4.3% probability of striking the Moon in 2032. Such an impact, with equivalent kinetic energy of ∼6.5 Mt TNT, is expected to produce a ∼1 km crater on the Moon, and will be the most energetic lunar impact event ever recorded in human history. Despite the associated risk, this scenario offers a rare and valuable scientific opportunity. Using a hybrid framework combining Monte Carlo orbital propagation, smoothed particle hydrodynamics (SPH) impact modeling, and N-body ejecta dynamics, we evaluate the physical outcomes and propose the observation timelines of this rare event. Our results suggest an optical flash of visual magnitude from -2.5 to -3 lasting several minutes directly after the impact, followed by hours of infrared afterglow from ∼2000 K molten rock cooling to a few hundred K. The associated seismic energy release would lead to a global-scale lunar reverberation (magnitude ∼5.0) that can be detectable by modern seismometers. Furthermore, the impact would eject ∼108 kg of debris that escapes the lunar gravity, with a small fraction reaching Earth to produce a lunar meteor outburst within 100 years. Finally, we integrate these results into a coordinated observation timeline, identifying the best detection windows for ground-based telescopes, lunar orbiters, and surface stations.
Abstract: "The near-Earth asteroid 2024 YR4 -- a ∼60 m rocky object that was once considered a potential Earth impactor -- has since been ruled out for Earth but retained a ∼4.3% probability of striking the Moon in 2032. Such an impact, with equivalent kinetic energy of ∼6.5 Mt TNT, is expected to produce a ∼1 km crater on the Moon, and will be the most energetic lunar impact event ever recorded in human history. Despite the associated risk, this scenario offers a rare and valuable scientific opportunity. Using a hybrid framework combining Monte Carlo orbital propagation, smoothed particle hydrodynamics (SPH) impact modeling, and N-body ejecta dynamics, we evaluate the physical outcomes and propose the observation timelines of this rare event. Our results suggest an optical flash of visual magnitude from -2.5 to -3 lasting several minutes directly after the impact, followed by hours of infrared afterglow from ∼2000 K molten rock cooling to a few hundred K. The associated seismic energy release would lead to a global-scale lunar reverberation (magnitude ∼5.0) that can be detectable by modern seismometers. Furthermore, the impact would eject ∼108 kg of debris that escapes the lunar gravity, with a small fraction reaching Earth to produce a lunar meteor outburst within 100 years. Finally, we integrate these results into a coordinated observation timeline, identifying the best detection windows for ground-based telescopes, lunar orbiters, and surface stations.