Discovery of 63 new young asteroid families

We searched for young asteroid families – those with ages $t_{\mathrm{age}}<10$ Myr and at least three members – using the proper element catalog from Nesvorný et al. (2024a). Our approach employed the Hierarchical Clustering Method (HCM) in a five-dimensional space of proper orbital elements: semimajor axis, eccentricity, inclination, proper nodal longitude, and proper perihelion longitude. The proper longitudes were calculated for various times in the past. Any convergence of these angles at times $t<10$ Myr ago was automatically identified by our algorithm as a clustering event in 5D space at time $t$. Using this method, we successfully recovered all previously known young families (over 40) and discovered 63 additional ones. The formation ages of these families were determined through backward orbital integrations. To validate orbital convergence, we applied three different methods and obtained generally consistent results. Notably, the vast majority of identified young families have the formation ages $t_{\mathrm{age}}\lesssim 1$ Myr. The number and properties of these families provide valuable constraints on the frequency of recent large cratering or catastrophic collisions, offering new insights into the ongoing collisional evolution of the main asteroid belt. Alternatively, at least some of the families identified here could have been produced by the spin-up and rotational fission of their parent bodies. Future studies should address the relative importance of collisions and rotational fission for young asteroid families identified here.