Earth Planets Space, Vol. 60 (No. 1), pp. 39-48, 2008
J. E. Thomas-Osip1, S. M. Lederer2,3, D. J. Osip1, F. Vilas3,4, D. Domingue5, K. Jarvis6, and S. L. Leeds2
1The Observatories of the Carnegie Institute of Washington, Las Campanas Observatory, Colina El Pino, Casilla 601, La Serena, Chile
2California State University San Bernardino
3NASA/Johnson Space Center
5Johns Hopkins University/Applied Physics Laboratory
6ESC Group/Hamilton Sundstrand
(Received October 31, 2006; Revised December 31, 2006; Accepted January 5, 2007; Online published February 12, 2008)
In 2004, Asteroid 25143 Itokawa made its final close approach to the Earth prior to its encounter with the Japanese spacecraft Hayabusa. This apparition was superb with Itokawa reaching magnitude 12 (two magnitudes brighter than the 2001 apparition and the brightest since its discovery in 1998) and covering a large range of observable solar phase angles. An extensive visible and near-infrared observing campaign of Itokawa was undertaken at Las Campanas and Lowell Observatories to obtain full rotational coverage and cover the largest possible range of solar phase angles (4-129°). Unresolved global color mapping over the complete light curve (best fit synodic period of 12.118 hr) shows no sign of rotational color variability with upper limits of a few percent across the full U-thru-K spectrum. These combined multi-wavelength (UBVRIJHK) rotational light curves allow for the concrete deconvolution of shape from albedo variation in the rotational models and as required for Hapke modeling presented in Paper II (Lederer et al., this issue), permits the removal of the rotational light curve effects from the solar phase curve. Furthermore, these derived solar phase curves can be fit with the IAU H,G magnitude system (Bowell et al., 1989) thus allowing the calculation of geometric albedos (pv = 0.23 ± 0.02) as well as an estimate of the asteroid's elongated shape (a/b = 1.9 ± 0.1) via the amplitude-phase relationtionship (Zappalá et al., 1990). Results derived from the extensive ground-based campaigns are compared and contrasted with the much higher spatial resolution in situ measurements made by the Hayabusa spacecraft. The 'ground-truth' provided by the Hayabusa mission results shed light on the inferences that can begin to be made for the general asteroid population.
Key words: Asteroid Itokawa, near-Earth objects, spectrophotometry.