The meteorite analogs of (65803) Didymos and implications for its origin

Context. Identifying meteorite analogs of asteroids is key to understanding their origin and evolution, evaluating planetary defense, and exploring potential space resources. The Didymos binary asteroid system, whose satellite Dimorphos was impacted by the Double Asteroid Redirection Test (DART) mission and will be further investigated by Hera, remains debated in terms of its meteorite analog. In addition, few studies have linked the spectral variations caused by the DART impact to meteorite analogs. Aims. This study determines the mineralogical composition and meteorite analog of the Didymos system. It also seeks to investigate the differences between the spectral effects of grain size and space weathering among different types of meteorites, and to use these relationships to interpret the spectral variations observed in the Didymos system. Methods. We used self-established calibration equations to infer the surface composition of Didymos from its spectral data. Band parameters and mineralogical parameters were derived and compared with meteorite samples. Results. The derived band parameters and mineralogical estimates indicate that Didymos is most consistent with L ordinary chondrites, favoring type 6, with an LL subtype being less likely. For H and L chondrites, ratio spectra can help assess whether the slope variations in the asteroid system or surface are primarily dominated by the grain size effect. However, for LL chondrites, the situation is more complex, as these two effects cannot be easily distinguished. The spectrum-estimated exposure age of Didymos (~0.39 Myr) is consistent with the surface crater retention age of Dimorphos. Conclusions. Didymos most likely originates from the highly metamorphosed inner regions of the L chondrite parent body. Based on this identification, the spectral variations in the Didymos system are interpreted as being dominated by space weathering rather than by grain size or compositional differences. The exposure age of Didymos further supports a rotational fission origin for the binary system.