Asteroid 25143 Itokawa and Other Small Bodies


Itokawa is an S-class Near-Earth asteroid with dimensions of 535 m × 294 m × 209 m that was visited by the Hayabusa spacecraft in 2005. The surface geology of Itokawa can be divided into two major units on the basis of surface appearance. Rough terrain, visibly characterized by a relatively high density of large, angular rocks or blocks, covers roughly 80% of Itokawa’s surface. Rough-terrain areas are generally located in regions of high gravitational potential (high geopotential elevation and low gravity) and have been referred to collectively as the “highlands”. Smooth terrain covers the remaining 20% of the asteroid, and is characterized by a high density of coarse grains 1–5 cm in diameter with only a few large blocks present. Smooth-terrain areas, here called lowlands, akin to the low regions mentioned in other studies, are generally located in regions of low gravitational potential (low geopotential elevation and high gravity). 

This study compares the size–frequency distribution (SFD) of small- to intermediate-sized blocks (0.1 to 5 m) on Itokawa to the SFD of large blocks (≥ 6 m) reported in previous studies. We regionally map and measure small to intermediate blocks and report the observed SFDs.  we compare these regional SFDs to global and regional SFDs of the large block population, and investigate relationships to factors such as surface elevation relative to Itokawa’s geoid and or regional slope.  Our efforts are to verify and extend these prior efforts, including looking at transitions in the SFDs with block size, that can lead to insights on which block sizes are mobilized on Itokawa. Our objective is (1) to provide observational constraints for the surface process acting on Itokawa for interpreting the history of other small asteroids similar to Itokawa in size (<1 km) and  (2) to explore potential mechanisms of remobilization of small particles in low-gravity environments. 

Other projects examined the potential lineament structure on Itokawa (which only further confirmed it was a rubble pile) and some potential use to study block movement as a proxy for directly measuring asteroid internal structure ("photoseismology").
AMICA image ST_2539423137, with the polygons outlining the highlands unit (cyan) and the lowlands unit (dark blue) and the SFD of the two units. The rollover at a higher value of D in the highlands shows that these data for this unit are complete.

Publications


Block Mapping and Analysis on Cometary Nuclei: Identifying and Quantifying Surface Change Due to Outgassing


J. L. Noviello, E. Asphaug


Lunar and Planetary Science Conference, Lunar and Planetary Science Conference, 2015 Mar, p. 2873


Comparing block populations across small bodies


C. Ernst, O. Barnouin, J. Noviello, M. Daly


K. Muinonen, A. Penttilä, M. Granvik, A. Virkki, G. Fedorets, O. Wilkman, T. Kohout, Asteroids, Comets, Meteors 2014, 2014 Jul, p. 151


Are There Structural Lineaments on Itokawa?


O. S. Barnouin, J. L. Noviello, C. M. Ernst


Lunar and Planetary Science Conference, Lunar and Planetary Science Conference, 2014 Mar, p. 2221


Block Distribution on Itokawa: Implications for Asteroid Surface Evolution


J. L. Noviello, C. M. Ernst, O.~S. Barnouin, M. Daly


Lunar and Planetary Science Conference, Lunar and Planetary Science Conference, 2014 Mar, p. 1587