Insights into the Size and Number of CM Chondrite Parent Bodies from Thermal Modelling and Links to Asteroids

CM chondrites are some of the most abundant meteorites and record evidence of aqueous alteration, thermal metamorphism and impacts on their parent bodies. Determining the size and number of CM chondrite parent bodies could shed light on the evolution of hydrated asteroids and how common CM-like material was in the early Solar System. Here, we combine thermal evolution modelling with the peak temperature distribution in the CM chondrite catalogue to constrain the parent body's early thermal history. In addition, we perform ultraviolet–visible–near-infrared (UV-vis-NIR) spectral comparisons to asteroids to understand the parent body's later collisional evolution. The timing of aqueous alteration and the number of heated CM chondrites is consistent with ≳50 km, low-temperature, aqueously altered parent body(ies) thermally metamorphosed by impacts. Spectra link the CM chondrites to hydrated, low-density asteroids and, combined with dynamical matches, limits the radii of surviving parent body(ies) to less than 150 km. Thermal modelling cannot determine the number of parent bodies, but the number of asteroids that are spectral or dynamical matches to CM chondrites supports that there were multiple parent bodies. Overall, our results suggest that one or more 50–100 km-radius planetesimals that accreted 3.5–4 Myr after calcium–aluminium-rich inclusion (CAI) formation could have produced the CM chondrites.