Craters on Asteroid Dinkinesh: Implications for Surface Age and Collisional Evolution

Kurzfassung

The NASA Discovery-class Lucy mission [1] performed its first asteroid flyby on November 1st, 2023. The target was the small Main Belt asteroid (MBA) (152830) Dinkinesh, with a semi-major axis of 2.19 AU, eccentricity of 0.11, inclination of 2.1 deg. Pre-encounter ground-based spectroscopy revealed that Dinkinesh has a S-type composition [2], and a mean diameter of 0.66-1.36 km [3]. The reconstructed Lucy trajectory indicates a close approach distance of 431 km, and a relative velocity of 4.5 km/s. All instruments successfully acquired scientific data, including the high-resolution camera L’LORRI (5 microrad/px [4]), revealing that Dinkinesh is a binary system. The primary has a top-like shape, analogous to recently visited asteroids like Bennu, Ryugu, and Didymos, with an average diameter of ~720 m. Its satellite, named Selam, has two lobes, each are ~220 m in diameter. Dinkinesh is the smallest MBA visited by spacecraft, and therefore provides an opportunity to study small asteroids in the Main Belt before they possibly become near-Earth asteroids (NEAs). Several NEAs with sizes similar to Dinkinesh have been visited (e.g., Bennu, Ryugu, Didymos), allowing for a direct comparison in terms of cratering histories. Of particular interest is the comparison with the Didymos binary system [e.g., 5] for its similar size and spectral type, and the presence of a satellite. In this work, we present Dinkinesh crater mapping based on a sequence of L’LORRI images near close approach. We also present a similar analysis for one of Selam’s lobe.