Simulating regolith deposition on 25143 Itokawa and other small asteroids
- Paper number
IAC-05-A3.P.06
- Author
Ms. Serina Diniega, University of Arizona, United States
- Coauthor
Dr. Hajime Yano, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan
- Year
2005
- Abstract
Studying regolith deposition yields an opportunity to learn about an asteroid’s interior and surface characteristics based on surficial appearance. However, small asteroids have very low escape velocities and typically are irregular shapes, thus making it difficult to do simple physical analyses. Computer simulations which numerically integrate equations describing the creation and placement of regolith particles provide better analyses, as from the simulation results general trends in the amount and placement of regolith on an asteroid can be inferred. The simulations discussed here integrate impact ejecta particle trajectories over a specified time period, to see if and where the ejecta will reimpact and contribute to the regolith layer. These trajectories are described by equations of motion which take into account the asteroid’s gravitational and rotational forces. Parameters such as ejecta velocity and size are derived from the cratering dynamics, which are dictated by the asteroid’s surface and internal properties. Many different parameter values are possible, as small asteroid bodies can have a wide range of physical and compositional properties, and can fall almost anywhere in the strength- and gravity-dominated regimes. Thus, simulations have been run with different types of interiors, such as fractured monoliths or rubble-piles, and surface environments have been considered and compared. This type of comparison, when combined with observational data, helps to put constraints on an asteroid’s parameter values. The development of the current model was begun at JAXA, specifically for application to 25143 Itokawa, which has recently been observed and measured by JAXA’s Hayabusa spacecraft. In that work, asteroids were approximated as a tri-axial ellipsoid, and consisted of a fractured solid interior and a loose regolith surface. Regolith deposition was found to occur primarily in the same region as the impact; i.e., a polar impact resulted in a primarily polar deposit. This would result in a fairly uniform global regolith deposit on larger asteroids (Eros-sized), unless a dominant regolith-creating impact had occurred recently. Small asteroids (Itokawa-sized) should exhibit very localized small deposits. However, the above results relied upon many extrapolations of observed cratering dynamics of porous/fractured material. In particular, very low (and currently unobserved) ejecta speeds are needed for any regolith to be retained on 25143 Itokawa, due to its very low surface gravity. Thus, further analyses have been done regarding the sensitivity of the cratering dynamics to the surface and internal properties of the asteroid, and the ability of different cratering regimes to create very low velocity ejecta speeds. In addition, comparisons have been made between observations of 25143 Itokawa and simulation results. These comparisons allow for further refinement of the simulation, as well as provide information about 25143 Itokawa’s probable interior and surface structure and the deposition of regolith on other small asteroids.
- Abstract document
- Manuscript document
IAC-05-A3.P.06.pdf (🔒 authorized access only).
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