Imminent impactors are small asteroids discovered a few hours before impact, and their identification is constantly monitored by the ESA Meerkat system. The last one – now designated as 2026 RW1 – was spotted on 6 September 2026 about 5 hours before impact by the Catalina Sky Survey, and it entered the atmosphere above the Indian ocean, with an impressive derived low uncertainty smaller than 100 meters on the entry point.

A new tool developed at the ESA NEO Coordination Centre can now forecast where the fragments of an incoming imminent impactor will fall. The tool allows the computation of strewn fields without the need of direct observations of the fireball, and over areas which are not covered by all-sky cameras.

Starting from the entry state at 100 km altitude computed from the orbital data, the model numerically propagates the entry through the atmosphere, simulating aerodynamic drag, ablation, and a cascading, statistically-driven fragmentation process. The many uncertainties of the problem are taken into account using a Monte Carlo approach. Each simulated fragment is tracked independently through breakup and dark flight, using real-time wind and atmospheric data forecasts from the Global Forecast System, down to where it lands. The model gave reliable predictions for past imminent impactors, such as 2008 TC3, 2023 CX1 (see the picture below), and 2024 BX1.

This new internal tool has been integrated directly into the NEOCC operational chain for imminent impactors. When Meerkat flags a newly discovered object with a significant impact probability, the Aegis system first refines its orbit and impact corridor. Once the impact is certain and well constrained, this new module automatically generates a strewn field map and sends the results to the NEOCC teams, all within the same automated pipeline, and normally within a few hours of warning time. Whenever additional observations are available the process is repeated, and the precision of the determined trajectory and the size of the strewn field are improved.

For the NEOCC and the broader planetary defence community, this addresses a long-standing gap. For the first time, a landing area for meteorite fragments can be produced before an object even reaches the atmosphere. This supports civil-protection decision-making when object size and predicted hazard warrant it, and aids prompt meteorite search campaigns to minimize terrestrial contamination of freshly fallen material.

Reference paper: Moscati et al., 2026. From orbit to ground: Pre-impact meteorite strewn field predictions for imminent impactors and meteorite recovery, Icarus, 461

Predicted pre-impact strewn field of imminent impactor 2023 CX1, computed using the last set of observations present on the NEOCP before the impact (0.8 h before atmospheric entry). The red, yellow, and white curves correspond to 99%, 80%, and 50% cumulative probability boundaries, respectively. The colour of the map corresponds to the spatial impact probability density per cell. The location of the recovered meteorites, indicated by crosses, are superimposed to the predicted strewn field. The colour of the cross represents the mass of the recovered meteorite fragment.