Observation Timelines for the Potential Lunar Impact of Asteroid 2024 YR4

TL;DR

The study analyzes a potential 2032 lunar impact by asteroid 2024 YR4, combining Monte Carlo orbital propagation, SPH impact modeling, and N-body ejecta dynamics to predict a $\sim$1 km lunar crater, a global moonquake near magnitude $M_{\rm seismic}\approx5.0$, and $\sim10^{7}$–$10^{8}$ kg of escaping ejecta. A high-lidelity framework links an initial optical/NIR flash with a long-lasting infrared afterglow, seismic signals, and Earth-bound debris, establishing a concrete, time-ordered observation plan across ground-based, lunar, and space platforms. The results quantify Earth-delivery probabilities for ejecta, secondary lunar impacts, and potential meteorite returns, guiding meteorite recovery and planetary-defense experiments while enabling a comprehensive cross-validation of impact physics and lunar interior properties. The work also provides a reusable blueprint for rapid-response observations of future impacts, turning a hazard into a multi-disciplinary opportunity for planetary science and public safety.

Abstract

The near-Earth asteroid 2024 YR4 -- a $\sim$60 m rocky object that was once considered a potential Earth impactor -- has since been ruled out for Earth but retained a $\sim$4.3% probability of striking the Moon in 2032. Such an impact, with equivalent kinetic energy of $\sim$6.5 Mt TNT, is expected to produce a $\sim$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 $\sim$2000 K molten rock cooling to a few hundred K. The associated seismic energy release would lead to a global-scale lunar reverberation (magnitude $\sim$5.0) that can be detectable by modern seismometers. Furthermore, the impact would eject $\sim$10$^8$ 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.

Figures (4)

• Figure 1: Map of the Moon’s entire surface showing the 4.3% 2024 YR4 impact corridor (with impact angle) and the dawn/dusk terminator (orange) on 22 December 2032 at 15:19 UTC. Six representative impact sites are highlighted, with their coordinates and impact angles listed in the bottom legend.
• Figure 2: SPH outcomes for three incidence angles ($36^\circ$, $60^\circ$, $84^\circ$). Top row: crater cross‐sections at late time ($t\sim$200 s) showing size and depth differences. Bottom row: plan‐view ejecta patterns on the lunar surface, illustrating transition from near‐radial symmetry at $36^\circ$, to asymmetric butterfly rays at $60^\circ$, then to sparse wing-shaped ejecta landing points at $84^\circ$. The central black area marks the impact crater, and the region to the left of the red dashed line denotes the zone of avoidance (ZoA) with no ejecta relatively.
• Figure 3: Time evolution of ejecta fractions impacting Earth (a) and the Moon (b), or remaining within 0.05 AU of Earth (c). The time axis is split into linear (first 100 days) and logarithmic (up to 100 yr) scales. In (a), the left panel uses a broken y-axis to better display the low fractions from Craters C–F.
• Figure 4: Predicted global distribution of surviving meteorite mass delivered to Earth over the first two years post-impact (T0 to T0 + 2 yr). The panels map the expected cumulative mass within each grid cell, projected onto a standard world map, for the six source craters.