The TRANSient NEO population: asteroids, comets or none of the above?

The classical distinction between asteroids (rocky and inert), and comets (ice-rich and active) has been blended in the last 15 years, leading to a more nuanced picture. Both classes are now believed to be simply end-members of a physical and dynamical continuum. The study of TRANSient NEOs (Near-Earth Objects showing characteristics of both classes) could be the missing link to understanding this new paradigm of small bodies continuum. We decided to investigate the TRANSNEO population because i) their repeated passages around the Sun make it in principle easier to detect a potential activity; ii) they can be extremely accessible for observations and a future space mission; iii) activity on NEO surfaces has been recently discovered even on apparently inactive places, thus attracting the interest of various space agencies. One of these intriguing bodies (3200 Phaethon) will indeed be the target of the JAXA DESTINY+ space mission, scheduled to be launched in 2025.In 2022, we started a new project called TRANSNEO financed by the Italian National Institute for Astrophysics (INAF) to characterize via spectroscopy, photometry, and polarimetry these bodies that often both show the asteroid/comet designation. We will present the latest results of the TRANSNEO project and put it in the larger context of active bodies in the Solar System.Acknowledgments: This research was funded by the Italian National Astrophysical Institute (INAF) - Call for Fundamental Research 2022. E.D. acknowledges the support from the ASI (ASI-INAF agreement AC n. 2022-1-HH.0).