Regolith Migration and Sorting on Asteroid Itokawa

Abstract

High-resolution images of the surface of asteroid Itokawa from the Hayabusa mission reveal it to be covered with unconsolidated millimeter-sized and larger gravels. Locations and morphologic characteristics of this gravel indicate that Itokawa has experienced considerable vibrations, which have triggered global-scale granular processes in its dry, vacuum, microgravity environment. These processes likely include granular convection, landslide-like granular migrations, and particle sorting, resulting in the segregation of the fine gravels into areas of potential lows. Granular processes become major resurfacing processes because of Itokawa's small size, implying that they can occur on other small asteroids should those have regolith.

Space weathering trends among carbonaceous asteroids

“…Indeed, spacecraft observations of small asteroids such as Eros and Itokawa reveal surfaces dominated by gravel and meter sized boulders with fines constricted to low potential zones Miyamoto et al 2007). These rocky surfaces are hypothesized to be more resistant to gardening processes (Chapman 2002;Willman et al 2010), thus space weathering effects (decreased albedo and band depths) are likely to be more prevalent on small objects with time.…”

Simulating Asteroid Rubble Piles With a Self-Gravitating Soft-Sphere Distinct Element Method Model

“…Further, it is possible to simulate and track the transmission of forces through grains which allows for exploration and simulation of seismic wave transmission and internal stress and pressure computations (Goldshtein et al 2002;Nishida & Tanaka 2010;Harada et al 2003;Wada et al 2006;Mouraille & Luding 2008;Agnolin et al 2005). Given the current accuracy of measured asteroid models and the evidence that they are "rubble-pile" bodies (Fujiwara et al 2006), the application of such mechanically precise Granular Dynamics simulations is justified and needed (Thomas & Robinson 2005;Richardson et al 2004;Miyamoto et al 2007). …”

Electrical Activity and Dust Lifting on Earth, Mars, and Beyond

“…6). Moreover, it shows that none of the smallest particles stay on top of boulders without being supported by other particles (Miyamoto et al, 2007). The high-resolution images also show craters with flat floors filled with fines.…”

“…The larger particles, on the other hand, are trapped by the asteroids' gravitational field, but can migrate from sunlit areas to shadows. During these migrations the larger particles can get trapped in topographic lows, as observed (Miyamoto et al, 2007). This hypothesis can be tested with measurements of particle size, kinetic energy, and electric fields at the surface of asteroids .…”

“…These findings suggest that the smallest particles migrate to gravitationally stable areas. Miyamoto et al (2007) suggests that vibrations forced by impacts, tides and thermal fluctuations are responsible for these global migrations. We disagree with them because electrostatic lifting of surface particles can easily explain the global migrations to low terrains.…”