Block distributions on Itokawa

Asteroid 25143 Itokawa is a small elongated asteroid with two distinct parts. The evolution of this two-part body has been the source of speculation. The scenarios for the formation of this asteroid include: two-body capture, catastrophic disruption and rapid reaccretion, YORP spin-up and mass shedding, and disruption (or partial disruption) with two-body reaccretion. In this paper we use the global and regional analyses of block populations and size–frequency distributions as evidence of the probable evolutionary history of Itokawa. The block sample used in this study is believed to be complete for blocks of size >6 m and consists of a sample more than twice as large as previous known studies. gh block size-frequency distributions hint at different evolutionary paths for the head and the body, their differences are not statistically significant. The distribution of blocks across each body provides clues as to the histories of each body. The head is populated in a spherically symmetric fashion while the body has a distinct equatorial peak. When considering that the head and the body may have been separate entities for a period of time and estimating a rotational axis using minimum rotational energy considerations, the preferential equatorial distribution becomes even more pronounced. We interpret this as excellent evidence for the partial disruption of a proto-Itokawa, subsequent planarization of a debris field and reaccretion of the head and the body into its present configuration.