Aging in space: Space weathering age of S-type and V-type asteroid families from the Sloan Digital Sky Survey

Space weathering (SW) progressively modifies the optical properties of bodies with no atmosphere, enabling surface exposure ages to be inferred from time-dependent spectral changes. In this study, we develop a machine-learning framework based on a support vector regression (SVR) model to estimate the SW age of S-type and V-type asteroid families from visible reflectance spectra. The SW age is defined as the time since an asteroid has been exposed to the interplanetary environment after a breakup or resurfacing event. We trained and validated the SVR model on laboratory SW simulations (H+ irradiation and laser pulse irradiation) using published reflectance spectra of olivine, pyroxene, and olivine-pyroxene mixtures and chondritic meteorites representative of S-type and V-type asteroid composition. We applied the model to Sloan Digital Sky Survey photometric data to estimate SW ages for ten S-type asteroid families and Vesta family. The model yielded SW age distributions that show broad agreement with dynamical family ages for Flora and Vesta, suggesting a quasi-steady evolution after family formation where SW and resurfacing operate in approximate balance. These inner-belt systems are consistent with frequent but shallow Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP)-driven regolith reworking, which does not fully reset spectral maturity. In contrast, Eunomia, Maria, and Koronis exhibit systematically younger SW ages relative to their dynamical ages, indicating more efficient surface renewal and/or slower weathering at larger heliocentric distances combined with episodic resurfacing on timescales of 10^8 years. Asteroid surface evolution reflects the interplay between SW efficiency, YORP-driven regolith redistribution, family formation mechanisms, and composition. In the inner belt, regolith reworking may preserve spectral maturity, whereas differences in resurfacing and weathering conditions across the mid- and outer belt may contribute to the decoupling of SW and dynamical ages. The SW age therefore provides an effective measure of surface maturation rather than a direct proxy for absolute age.