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PS: Regolith ejection on the asteroid Didymos due to its fast rotation – Trógolo

April 18 @ 12:30 pm 12:45 pm CMT

(65803) Didymos is the binary Near Earth Asteroid target of the DART (NASA)/LICIA (ASI) andHera (ESA) missions. It orbits the Sun with a semi-major axis of 1.64 AU, and it is made of a 780m diameter primary body (Didymos) and a 160 m satellite (Dimorphos), orbiting the primary witha semi-major axis of 1180 m and an orbital period of 11.9 h. The primary has a rotation period of2.26 h, very close to the limit of structural stability. The low density estimated for Didymos, 2170kg/m3, shows that it is not a monolithic body, will have high macro-porosity, typical of gravitationalaggregates (or rubble-piles) and it also shows an equatorial bulge, like top-shape asteroids Ryuguand Bennu. Local acceleration near Didymos’ equatorial region may be directed outwards, allowingregolith to leave the surface. In this work, we study the dynamics of particles that are ejected fromthe surface of Didymos when the centrifugal acceleration is large enough to overcome local gravity.The analysis is carried out with a numerical code that integrates the particles’ equation of motion in anon-inertial rotating frame of reference, centered on the primary asteroid. A polyhedral shape modelfor Didymos is considered, formed by 1000 vertices and 1996 triangular faces, at which center, sampleparticles are placed. The environment of the asteroid is studied by computing the radial density ofparticles, assuming -as an arbitrary reference- an ejection mass rate of 1 kg/s. We found that thedensity of mass in orbit is strongly dependent on the physical parameters of the system, like Didymos’density. Since the mass (m) and volume (V) are not well determined, we perform different simulationsadopting different pairs of values for m and V in order to determine under what conditions it is possible to obtain a cloud of particles around the asteroid.

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