Icarus 194 (2008) 137–145 www.elsevier.com/locate/icarus Near-infrared spectrophotometry of Asteroid 25143 Itokawa from NIRS on the Hayabusa spacecraft Kohei Kitazato a,b,∗ , Beth E. Clark c , Masanao Abe b , Shinsuke Abe d , Yasuhiko Takagi e , Takahiro Hiroi f , Olivier S. Barnouin-Jha g , Paul A. Abell h , Susan M. Lederer i , Faith Vilas j a Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan b Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan c Physics Department, Ithaca College, 953 Danby Road, Ithaca, NY 14850, USA d Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, Hyogo 657-8501, Japan e Toho Gakuen University, 3-11 Heiwagaoka, Meito, Nagoya, Aichi 465-8515, Japan f Department of Geological Sciences, Brown University, Providence, RI 02912, USA g The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723-6099, USA h NASA, Johnson Space Center, Houston, TX 77058, USA i Department of Physics, California State University, San Bernardino, CA 92407, USA j MMT Observatory, University of Arizona, Tucson, AZ 85721, USA Received 18 February 2007; revised 13 August 2007 Abstract A photometric analysis of the S-type Asteroid 25143 Itokawa is performed over multiple wavelengths ranging from 0.85 to 2.10 μm based on disk-resolved reflectance spectra obtained with the Hayabusa near-infrared spectrometer (NIRS). We derive the global photometric properties of Itokawa in terms of Hapke’s photometric model. We find that Itokawa has a single-scatter albedo that is 35–40% less than that of Asteroid 433 Eros. Itokawa also has a single-particle phase function that is more strongly back-scattering than that of Eros. Despite its hummocky surface strewn with large boulders, Itokawa exhibits an opposition effect. However, the total amplitude of the opposition surge for Itokawa was estimated to be less than unity while Eros and other S-type asteroids have been found to have model values exceeding unity. The wavelength dependence of the opposition surge width reveals that coherent backscatter contributes to the opposition effect on Itokawa’s surface. The photometric roughness of Itokawa is well constrained to a value of 26 ◦ ± 1 ◦ which is similar to Eros, suggesting that photometric roughness models the smallest surface roughness scale for which shadows exist.  2007 Elsevier Inc. All rights reserved. Keywords: Asteroid Itokawa; Photometry; Spectrophotometry 1. Introduction The near infrared spectrometer (NIRS) instrument of the Hayabusa spacecraft obtained more than 80,000 surface-re- solved reflectance spectra of the near-Earth Asteroid 25143 Itokawa during the period of September 10 to December 24, 2005. Spectra from 0.76 to 2.25 μm were acquired over a wide * Corresponding author at: Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kana- gawa 229-8510, Japan. Fax: +81 42 759 8457. E-mail address: kitazato@planeta.sci.isas.jaxa.jp (K. Kitazato). range of incidence and emission angles and covering phase an- gles from 0.2 ◦ to 38.4 ◦ , allowing us to construct a spectropho- tometric model of the asteroid’s surface that could be used to derive physical properties of the asteroid’s surface and to cor- rect all NIRS spectra to a common viewing geometry. Light scattering on the surface of an atmosphereless So- lar System body can provide constraints on the physical and textural characteristics of the surface materials, such as sur- face roughness, porosity, and optical properties. Abundant disk- resolved data with different viewing geometries are essential to determine the photometric properties accurately, which is dif- ficult to obtain from ground-based observation (Domingue and 0019-1035/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.icarus.2007.08.029