Shape and Distribution of Rubble-pile Asteroid with Impact

Paper number

IAC-08.C1.1.1

Author

Mr. YUICHI MIWA, The University of TOKYO, Graduate school, Japan

Coauthor

Dr. Hajime Yano, Japan Aerospace Exploration Agency (JAXA), Japan

Coauthor

Dr. Mutsuko Morimoto, Japan Aerospace Exploration Agency (JAXA), Japan

Coauthor

Dr. Osamu Mori, Japan Aerospace Exploration Agency (JAXA), Japan

Coauthor

Dr. Junichiro Kawaguchi, Japan Aerospace Exploration Agency (JAXA), Japan

Year

2008

Abstract

This paper analyzes the shape and distribution of a rubble-pile asteroid using numerical simulations.

The spacecraft "HAYABUSA" performed observations of asteroid "ITOKAWA" including high resolution pictures. These observations show that ITOKAWA is a rubble-pile asteroid which consists of the rocks piled up by universal gravity. Its unique shape and regolith distribution are caused by composition of universal gravity, friction, centrifugal force by spin and impacts. These impacts are given by collisions of small falling particles. In this study, the behaviors of various size particles in the space are analyzed by numerical simulations using multi-particle model. A rubble-pile asteroid is modeled by particles including gravity, friction, centrifugal force and impulse force. The results are compared with the surface of ITOKAWA and the inferred internal structure of ITOKAWA is discussed. It can be applied to the other rubble-pile asteroids. If the internal structure and regolith distribution of the surface can be guessed from the asteroid shape, volume and rotation period without the effort to get close to it, this process will be a great advantage for asteroid research.

In this paper, the behaviors of particles which are oscillated on the ground are simulated first. When the various size particles are shaken, the Brazil-Nut effect occurs. It is generally known as the phenomenon that causes the larger particles to rise to the top of the shaken granular mixtures in a container. This phenomenon is confirmed by simulations. When the particle is in contact with the other particles, mass-spring-damper (MSD) model is applied. The motions of particles with changing the amplitude of shaking, oscillation period, the ratio of particles’ density and diameter are analyzed. The various conditions that Brazil-Nut effect occurs are obtained. 

Secondly, the behaviors of particles shaken by impacts in the space are simulated. These dynamics are different from those on the ground. In the space, the particles are not restrained by the container and universal gravity between each particle and centrifugal force by spin are considered instead of the earth gravity. The motions of particles are very complicated. In these conditions, the dynamics of them are analyzed by numerical simulation using multi-particle model.

Finally, the motions in the same condition with ITOKAWA are simulated. The results of simulations are compared with those of observations and the internal structure and constitution process of ITOKAWA are verified. 

Abstract document

IAC-08.C1.1.1.pdf

Manuscript document

IAC-08.C1.1.1.pdf (🔒 authorized access only).

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