Collision and gravitational reaccumulation: Possible formation mechanism of the asteroid Itokawa

Aims. We investigate the possibility that the observed sea-otter shape of the asteroid Itokawa, associated with the presence of big boulders on its surface, originates from the reaccumulation process that may have formed this asteroid, assuming that it consists of reaccumulated fragments from a catastrophically disrupted parent body. Methods. We computed the gravitational phase of an asteroid disruption, during which fragments can reaccumulate and form aggregates, using a version of the N-body code pkdgrav that includes a model of rigid aggregates. This new model allows the formation of non-idealized rubble piles as a result of reaccumulation that are made up of irregular, competent pieces. Shape and spin information of reaccumulated bodies are thus preserved by allowing fragments to stick on contact (and optionally bounce or cause further fragmentation, depending on user-selectable parameters), instead of merging into growing spheres. Results. We find that the reaccumulation process of an asteroid disruption can produce aggregates whose form is similar to that of Itokawa, and can lead to the deposit of big boulders on the surface, as observed on Itokawa.

[1]  Derek C. Richardson,et al.  Formation of Asteroid Families by Catastrophic Disruption: Simulations with Fragmentation and Gravitational Reaccumulation , 2003 .

[2]  D. Richardson,et al.  A Self-Consistent Numerical Treatment of Fractal Aggregate Dynamics , 1995 .

[3]  P. Tanga,et al.  Collisions and Gravitational Reaccumulation: Forming Asteroid Families and Satellites , 2001, Science.

[4]  W. Benz,et al.  Catastrophic disruption of pre-shattered parent bodies , 2004 .

[5]  W. Benz,et al.  Numerical simulations of impacts involving porous bodies: I. Implementing sub-resolution porosity in a 3D SPH hydrocode , 2008, 0807.1264.

[6]  Gareth S. Collins,et al.  A strain-based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets , 2006 .

[7]  Kevin R. Housen,et al.  Scale Effects in Strength-Dominated Collisions of Rocky Asteroids , 1999 .

[8]  Robert Jedicke,et al.  The fossilized size distribution of the main asteroid belt , 2003 .

[9]  P. Michel,et al.  Numerical simulations of granular dynamics: I. Hard-sphere discrete element method and tests , 2011, 1306.2528.

[10]  K. Holsapple.  Spin limits of Solar System bodies: From the small fast-rotators to 2003 EL61 , 2007 .

[11]  Erik Asphaug,et al.  Impact Simulations with Fracture. I. Method and Tests , 1994 .

[12]  Derek C. Richardson,et al.  Size-frequency distributions of fragments from SPH/N-body simulations of asteroid impacts: Comparison with observed asteroid families , 2007 .

[13]  J. Kawaguchi,et al.  The Rubble-Pile Asteroid Itokawa as Observed by Hayabusa , 2006, Science.

[14]  Knight,et al.  Vibration-induced size separation in granular media: The convection connection. , 1993, Physical review letters.

[15]  W. Losert,et al.  Granular convection in microgravity. , 2012, Physical review letters.

[16]  Derek C. Richardson,et al.  Numerical simulations of asteroids modelled as gravitational aggregates with cohesion , 2009 .

[17]  Willy Benz,et al.  Numerical simulations of impacts involving porous bodies: II. Comparison with laboratory experiments , 2009 .

[18]  Kazuya Yoshida,et al.  Touchdown of the Hayabusa Spacecraft at the Muses Sea on Itokawa , 2006, Science.

[19]  Derek C. Richardson,et al.  Disruption of fragmented parent bodies as the origin of asteroid families , 2003, Nature.

[20]  W. Benz,et al.  Catastrophic Disruptions Revisited , 1999 .

[21]  George Lake,et al.  Direct Large-Scale N-Body Simulations of Planetesimal Dynamics , 2000 .

[22]  Derek C. Richardson,et al.  Experimental determination of the coefficient of restitution for meter-scale granite spheres , 2011 .

[23]  Derek C. Richardson,et al.  The formation of asteroid satellites in large impacts: Results from numerical simulations , 2004 .