Mass and Local Topography Measurements of Itokawa by Hayabusa

Abe, Shinsuke
Mukai, Tadashi
Hirata, Naru
Barnouin-Jha, Olivier S.
Cheng, Andrew F.
Demura, Hirohide
Gaskell, Robert W.
Hashimoto, Tatsuaki
Hiraoka, Kensuke
Honda, Takayuki
Kubota, Takashi
Matsuoka, Masatoshi
Mizuno, Takahide
Nakamura, Ryosuke
Scheeres, Daniel J.
Yoshikawa, Makoto

¹Graduate School of Science and Technology, Kobe University, Nada, Kobe 657-8501, Japan. ²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA. ³Department of Computer Software, University of Aizu, Aizuwakamatsu, Fukushima 965-8580, Japan. ⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA. ⁵Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan. ⁶NEC Aerospace Systems Co. Ltd., Fuchu, Tokyo 181-8551, Japan. ⁷National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan. ⁸Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109-2140, USA.

*To whom correspondence should be addressed. E-mail: [email protected]

15 February 2006; accepted 21 April 2006

10.1126/science.1126272

Science 312(5778):p 1344-1347, June 2, 2006.

The ranging instrument aboard the Hayabusa spacecraft measured the surface topography of asteroid 25143 ltokawa and its mass. A typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 Eros, which suggests a surface structure on Itokawa similar to crater ejecta on Eros. The mass of Itokawa was estimated as (3.58 ± 0.18) × 10¹⁰ kilograms, implying a bulk density of (1.95 ± 0.14) grams per cubic centimeter for a volume of (1.84 ± 0.09) × 10⁷ cubic meters and a bulk porosity of ∼40%, which is similar to that of angular sands, when assuming an LL (low iron chondritic) meteorite composition. Combined with surface observations, these data indicate that Itokawa is the first subkilometer-sized small asteroid showing a rubble-pile body rather than a solid monolithic asteroid.