First results from the first two years of NEA spectroscopic observations within the NEOPOPS project at Asiago Observatory

Introduction: Near-Earth Asteroids (NEAs) are asteroids with perihelion distances smaller than 1.3 AU. They represent a key population for the study of small bodies, Solar System evolution, and the possible delivery of water and organic molecules to the early Earth (Kokhirova et al. 2023)]. A subset of NEAs, the Potentially Hazardous Asteroids (PHAs), follows orbits that can approach the Earth and includes objects large enough to produce significant damage in the event of an impact. At present, about 2500 PHAs are known, including objects such as Didymos and Apophis. For these reasons, the physical characterization of NEAs, and in particular PHAs, is an important task for both Solar System science and planetary defence.

The NEOPOPS project: Space missions provide detailed information on selected targets, but ground-based observations remain the main tool for the rapid physical characterization of newly discovered NEAs. As of May 2026, more than 41,000 NEAs are known, with an average discovery rate of about 3000 new objects per year. The NEO Physical Observations and Properties Simulation project (NEOPOPS) is funded by the Horizon Europe Programme, implemented by ESA and led by INAF–OAR. The project started in February 2025 and will continue until August 2028. Its goal is to improve the physical characterization rate of NEAs through complementary techniques, including photometry, spectroscopy, and polarimetry, with particular attention to rapid response observations of newly discovered objects and possible impactors.

Observations: In this work, we present the first results from the first two years of the spectroscopic survey of NEAs carried out at the Asiago Observatory within Work Package 4, dedicated to spectroscopy, and Work Package 6, dedicated to rapid response observations. The observations were obtained with the 1.22 m Galileo Telescope equipped with the Boller & Chivens spectrograph, and with the 1.82 m Copernico Telescope equipped with the AFOSC spectrograph. These facilities allow low-resolution visible spectroscopy in the approximate range 0.45–1.0 μm, depending on the telescope and instrumental setup. Since the beginning of the project, 75 NEAs have been observed, including recently discovered objects, PHAs, and targets with available light-curve information.

Analysis and results: The spectral analysis includes taxonomic classification based on the DeMeo et al. (2009) system, comparison with laboratory meteorite spectra (DeMeo et al. 2022), and the study of spectral slopes and absorption features. The observed sample is dominated by S-complex objects, followed by X- and C-complex asteroids. For each object, the taxonomic classification is also used to estimate the size when no direct measurement is available, assuming a representative albedo for the assigned taxonomic class. We also investigate the distribution of the observed NEAs as a function of absolute magnitude, estimated size, and orbital parameters, including perihelion distance, aphelion distance, eccentricity, inclination, and semi-major axis. This allows us to compare the spectroscopic properties of the sample with its dynamical distribution and to distinguish between NEAs and PHAs.

A preliminary analysis of the phase reddening effect was also performed by studying the spectral slope as a function of phase angle in two wavelength intervals, 6000–7000 Å and 5500–9000 Å. This analysis allows us to search for possible trends between surface spectral properties and observing geometry. Several objects were observed on different nights or over a significant fraction of their rotation, allowing us to test possible spectral variability. Among them, the binary asteroid 1999 HF1 was observed over two full rotations. We also obtained twelve spectra of the PHA 2025 FA22, classified as an X-type object, which show a largely homogeneous surface over about 2.3 hours of rotational coverage.

Conclusions: These first results show the role of regular spectroscopic monitoring from Asiago within the NEOPOPS project. The survey provides taxonomic and compositional information for a growing sample of NEAs, supports the rapid characterization of newly discovered objects, and allows the study of spectral variability in selected targets. The continuation of the survey will increase the statistical value of the sample and improve our knowledge of the physical properties of NEAs and PHAs.

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.

References
[1] Kokhirova et al. (2023), Solar System Research, 57, 487–495.
[2] DeMeo et al. (2009), Icarus, 202, 160–180.
[3] DeMeo et al. (2022), Icarus, 380, 114971.