Exploring rotational properties and the YORP effect in asteroid families

¹ Department of Physics and Astronomy, University of Padova, Padova, Italy
² JSPS International Research Fellow, Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan
³ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 November 2025
Accepted: 26 January 2026

Abstract

Context. The long-term dynamical evolution of asteroid families is governed by the interplay between orbital and rotational evolution driven by thermal forces and collision.

Aims. We aim to observationally trace the rotational evolution of main-belt asteroid families over gigayear timescales.

Methods. We analyzed rotational properties of 8739 asteroids with spin period measurements and 3794 asteroids with obliquity determinations across 28 asteroid families spanning ages from 14 Myr to 3 Gyr. We introduced a dimensionless timescale that normalizes each asteroid’s family age by its classical YORP timescale, enabling a direct comparison of the rotational states across different evolutionary stages. We examined two key observables: the fraction of slow rotators (periods greater than or equal to 30 hours) and the polarization fraction (the degree to which asteroid spin poles align correctly with their position in the family’s V-shape distribution according to the Yarkovsky theory). Evolution of both quantities were fit to identify characteristic transition timescales.

Results. We discovered that the slow-rotator fraction increases steeply with t and saturates at f_slow ≃ 0.25 around a break point of t_bp ≃ 20. This implies a stochastic YORP timescale of τ_YORP,stoc ≃ 10 τ_YORP in comparison with the rotational evolution models that include tumbling and weakened YORP torques. The polarization fraction reaches a maximum of ≃0.8 at t ≃ 16 and then decays toward the random limit f_pol → 0.5 for t ≳ 20, indicating an increasing dominance of collisional spin reorientation over time.

Conclusions. The rotation properties within different asteroid families offer crucial clues to rotation evolution and can serve as a new dimension for the age estimation of asteroid families, particularly as more data will become available in the era of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST).