Characterization of the virtual impactor by the NEOPOPS team: the case of 2025 FA22

The study of Near-Earth Objects (NEOs) is essential for several reasons. From a scientific perspective, these objects may have played a role in delivering organic material and water to Earth [1,2] while also preserving information about their origin and evolution from the early Solar System. From a planetary defense perspective, NEOs can pose a non-negligible threat to Earth. Several events in Earth’s history (e.g. K-Pg event and the Chelyabinsk meteor in February 2013) demonstrate that such objects can cause significant material damage and, in extreme cases, mass extinctions. In particular, previous studies have shown that even relatively small objects (10-100m in diameter) can produce regional-scale damage [3]. It is therefore essential to characterize these potential hazards by providing key information to support civil protection and mitigation efforts.

To address these scientific and operational challenges, the NEO Physical Observations and Properties Simulation (NEOPOPS) project was funded by the European Union and implemented by the European Space Agency (ESA). In particular, the Rapid Response work package (WP6) aims to enable the comprehensive characterization of potentially hazardous objects within a short time after discovery. Due to their small size, these objects are typically bright enough for detailed observations for only a few weeks. After this period, they generally become unobservable until their next predicted close approach or potential impact date.

2025 FA22 was discovered by the Pan-STARRS-2 survey on March 29, 2025. With an estimated diameter between 120 and 290 m, it was originally classified as a virtual impactor with a Torino Scale [4] rating of 1, due to a low but non-zero probability of impact in 2089. This initial risk classification triggered high-priority follow-up astrometry, which rapidly refined the orbit and conclusively ruled out any impact threat, leading to its removal from global risk lists. On September 18, 2025, 2025 FA22 passed safely by Earth at a distance of approximately 8.42 x10⁵ km (about 2.19 lunar distances). It was therefore selected as a primary target for a global, coordinated observing campaign under the auspices of the International Asteroid Warning Network (IAWN).

The campaign was specifically designed to stress-test the global planetary defense infrastructure, treating the object, for the purposes of the exercise, as a hypothetical virtual impactor. This opportunity also enabled the collection of extensive astrometric and physical characterization data. We successfully conducted a coordinated observational campaign, including astrometry, photometry, spectroscopy, radar and polarimetry, within just a few weeks of the initial alert. This rapid response demonstrates the capability to transition from discovery to a detailed physical characterization within the tight operational windows required for planetary defense.

In this presentation, we report the results of this extensive multi-technique observing campaign [5,6], providing a comprehensive set of physical parameters for 2025 FA22.

 

Acknowledgments : The NEOPOPS observations contract is funded by the Horizon Europe Programme of the European Union and implemented by ESA (agreement No. 4000147191/25/D/MRP). The observations with the 0.65m Mayer telescope were supported by the Praemium Academiae award from the Academy of Sciences of the Czech Republic, grant no. AP2401.

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• Ieva S., Bourdelle de Micas J., Farina A., et al., in prep