Density Inhomogeneity, YORP and Itokawa

Details Density Inhomogeneity, YORP and Itokawa Density Inhomogeneity, YORP and Itokawa

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....40.2839s&link_type=abstract

American Astronomical Society, DPS meeting #40, #28.39; Bulletin of the American Astronomical Society, Vol. 41, p.559

Astronomy and Astrophysics

Astronomy

Scientific paper

We hypothesize that the non-detection of YORP for the asteroid Itokawa (Durech et al., AA 488, 345-350, 2008) may be due to density inhomogeneities within that body. Our result is consistent with either the neck or head region of Itokawa having a larger bulk density than the remainder of the body. A density increase in the neck region could be ascribed to the accumulation of finer gravels, which have been shown to be migrating into this region of Itokawa (Miyamoto et al., Science 316, 1011-1014, 2007). Conversely, it may also be due to the ``head'' of Itokawa having a larger density, which would be consistent with the observed density contrast in the binary system 1999 KW4 (Ostro et al., Science 314, 1276-1280, 2006).
The effect of density inhomogeneities in an asteroid can alter the predicted YORP rate of change in angular velocity and obliquity. We apply these corrections to the Itokawa shape model and find that its YORP angular velocity rate is sensitive to offsets between its center of mass and center of figure, with a center of mass shift on the order of 15 meters being able to null out the YORP effect. Given the non-detection of YORP for Itokawa as of 2008, this implies that the magnitude of the YORP effect is reduced for that body, consistent with a center of mass shift towards the head/neck region. Eventual detection of the YORP effect for Itokawa should provide constraints on its density distribution. This theory could also be applied to asteroids visited by future spacecraft to constrain their density inhomogeneities.
This work was supported in part by grants from the NASA PGG and DDAP programs.

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