NEOPOPS – Ground based observations in support of the planetary defense

The NEO Physical Observations and Properties Simulations (NEOPOPS) project, funded by the European Space Agency (ESA) and led by INAF – OAR (Observatory of Rome) is dedicated to the physical characterization of Near-Earth Objects (NEOs). The study of these objects is essential for several reasons. From a science perspective, NEOs may have played a role in delivering organic material and water to Earth (Morbidelli et al., 2000; Marty et al., 2016), and thus preserve key information about their origin and evolution from the early Solar System. From a planetary defense standpoint, NEOs can also pose a significant threat to Earth. Several events in the Earth’s history (K-Pg impact, the Chelyabinsk fall in 2013 and more recently the alert triggered by 2024 YR4 in early 2025) demonstrate that this population can cause substantial material damage and, in extreme cases, mass extinctions.

To mitigate the risk posed by potentially hazardous objects, it is crucial to characterize them shortly after their discovery. The NEOPOPS project therefore conducts spectroscopic, photometric, and polarimetric observations using multiple telescopes, including the 3.58m TNG (La Palma, Spain), the 8.2m VLT (Cerro Paranal, Chile), the 1.54m Danish telescope (La Silla, Chile) and the 1.82m Copernico Telescopio (Asiago, Italy). Our goal is to constrain key physical parameters that may inform potential mitigation strategies in the event of a future impact threat.

This presentation focuses on the characterization of NEOs by spectroscopy, photometry, polarimetry and rapid response. We aim to obtain monthly observations of NEOs selected according to three prioritized criteria: (1) objects that pose a potential impact risk, identified in collaboration with the NEO Coordination Center (NEOCC, ESA-ESRIN), which issues alerts when a threat is detected; (2) NEOs that are targets of upcoming space missions; and (3) recently discovered NEOs, which are particularly challenging to observe because their visibility window may last only few weeks, after which they can remain unobservable for decades. The spectra obtained provide constraints on surface composition, possible surface heterogeneity, and other physical properties, and are shared across NEOPOPS observer team to enable a comprehensive characterization of each object.

For the rapid-response observations, the goal is to provide rapid, multi-technique observations to derive critical parameters relevant to impact mitigation planning. In the event of an alert, all the observing teams are mobilized to observe the object as quickly as possible. Triggered-alert objects may become unobservable shortly after discovery, often well before their predicted virtual impact date. In 2025, four alerts were issued, 2024 YR4, 2025 FA22, 2025 SC5, and 2025 VP2, with Torino Scale (Binzel et al., 2000) values ranging from 1 to 3. These real-case scenarios allowed us to test and validate our rapid response procedures and to derive key parameters, such as albedo, rotational period estimates, and surface composition.