Visible Spectroscopic Survey of Near Earth Objects/Potentially Hazardous Asteroids

On 26 September 2022 Dimorphos, the small satellite of the Potentially Hazardous asteroid (PHA) Didymos, has been deviated from its orbit by the NASA DART spacecraft. On April 13, 2029, the Earth will witness one of the rarest events, never documented in such detail before: the asteroid Apophis will pass within 33,000 km of Earth.Apophis is a PHA that had raised great concern at its first discovery due to the not remote possibility that it could impact our planet in 2029. Like Didymos-Dimorphos and Apophis, among the Near Earth Asteroids (NEAs), there are many other PHAs, none of the known ones causing concern for possible impacts with our planet in the next decades, but which nonetheless need to be carefully monitored and studied to understand their physical and dynamic characteristics. With this spirit, since several years we have started a spectroscopic observational campaign of NEOs, particularly of PHAs.In this work we present an update of our spectroscopic survey of Near Earth Objects (NEOs), performed with the Asiago Telescopes. The program was also part of the EU-funded NEO Rapid Observation, Characterization and Key Simulations (NEOROCKS) project, focused on the acquisition and analysis of data on newly discovered small size objects, possibly PHAs.The importance of NEOs is widely recognized as they can help to investigate the origin and evolution of the Solar System, in particular also the origin of life and water on Earth, they are possible future mining resources, but they are also possible threatening objects to our planet. This is particularly true for the PHAs, the subgroup of NEOs characterized by orbits that can make close approaches to the Earth and large enough to cause significant regional damage in the event of an impact. Indeed, Didymos and Apophis are only two of the about 2400 PHA known so far. So it is particularly important and urgent to know in detail the dynamical, physical, and compositional properties of as many PHAs as possible in order also to have the necessary information to establish mitigation strategies. The encounter with the binary system Didymos-Dimorphos by the Hera mission in 2027 and of Apophis by the NASA/Osiris-Apex and hopefully by the ESA/Rames missions in 2029, will be unique opportunities to study with great detail these individual peculiar objects. Both missions will produce fundamental information useful to investigate the whole class of PHAs. At the same time, our ground-based investigation of PHAs will be extremely useful to better understand this class of objects as a whole and contribute to better interpret the huge quantity of data that will be obtained of Didymos-Dimorphos and of Apophis from ground and from space. They will be also used as a statistical reference for the whole class. Therefore, the study of PHAs enables the improvement of our planetary defence capabilities and the mitigation of the risks of impact with Earth. Our observations are performed with the 1.22m Galileo Telescope equipped with a Boller & Chivens spectrograph and the 1.82m Copernico Telescope equipped with AFOSC (Asiago Faint Object Spectrograph and Camera), located at the Asiago Observatory, Italy, covering a spectral range between 0.4 - 1 micron. The observations of PHAs are particularly challenging because of their typical faintness and their high speed rate . Nevertheless, since the beginning of the project, January 2020, we have observed about 70 NEOs of which 28 PHAs. Some of them are newly discovered, with a size ranging from 30 m to about 900 m. Most of them have an unknown taxonomic classification or not a clear one yet assigned. We performed the taxonomic classification through a comparison with spectral types from Bus-Binzel Taxonomy [1] and with laboratory meteorites spectra from the Relab database. Up to now we can account different types of asteroids, spanning from carbonaceous C to silicate S, and also some rare types as O or B. Some objects (eg, 1988 OR2 and Didymos) have been observed during their rotational periods, allowing the study of their surface variegation. We will present the results of the observational campaign obtained so far