Oral Presentation
Clarification of Deformation Process of Asteroidal Shapes Through Impact Simulations: Constraint on Collisional History of Large Asteroids
Presenter: Keisuke Sugiura (Nagoya University, Graduate School of Science)
Irregular shapes of asteroids such as asteroid Itokawa are probably formed through collisional destruction of asteroids, and thus clarifying impact conditions to form various irregular shapes may lead to constrain formation environment or era of asteroids. We developed the simulation code of SPH method for elastic dynamics with the models of fracture of rock and friction of granular material, and reproduced impacts into rocky target asteroids with the diameter of 100 km. As a result of low-resolution simulations (totally 100,000 SPH particles) of equal-mass impacts with impact velocities of 50 – 400 m/s and angles of 5 – 45 degrees, we find that the largest remnants become various shapes (bilobed, spherical, flat, elongated, and hemispherical shapes) including extremely elongated or flat shapes. As a result of high-resolution simulations (totally 4 million SPH particles) of catastrophic destructions, we find that destructive impacts mainly produce spherical or bilobed shapes. Collisions with the mean impact velocity of the present main belt (~ 5 km/s) mainly result in catastrophic disruptions, which are difficult to form extremely irregular shapes. Collisional lifetimes of asteroids with diameters larger than 100 km are much longer than the age of the solar system. Thus the shapes of large asteroids may be formed in the primordial environment, where impact velocities may be < 1km/s because of the absence of large perturbers and such impacts with similar masses lead to the formation of extremely irregular shapes. Therefore, we suggest that extremely irregular shapes with the diameter larger than 100 km (such as (216) Kleopatra) are probably formed in the primordial environment and remain the same until today.
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