Lifted particles from the fast spinning primary of the Near-Earth Asteroid (65803) Didymos

Abstract

An increasing number of Near Earth Asteroids (NEAs) in the range of a few hundred metres to a few kilometres in size have relatively high spin rates, from less than 4 h, down to ∼ 2.2 h, depending on spectral type. For some of these bodies, local acceleration near the equator may be directed outwards so that lift off of near-equatorial material is possible. In particular, this may be the case for asteroid Didymos, the primary of the (65803) Didymos binary system, which is the target of the DART (NASA) and Hera (ESA) space missions. The study of the dynamics of particles in such an environment has been carried out – in the frame of the Hera mission and the EC-H2020 NEO-MAPP project – according to the available shape model, known physical parameters and orbital information available before the DART impact. The presence of orbiting particles in the system is likely for most of the estimated range of values for mass and volume. The spatial mass density of ejected material is calculated for different particle sizes and at different heliocentric orbit epochs, revealing that large particles dominate the mass density distribution and that small particle abundance depends on observation epoch. Estimates of take off and landing areas on Didymos are also reported. Available estimates of the system mass and primary extents, after the DART mission, confirm that the main conclusions of this study are valid in the context of current knowledge.