Abstract
Abstract 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 (p v = 0.23 ± 0.02) as well as an estimate of the asteroid’s elongated shape (a/b = 1.9 ± 0.1) via the amplitudephase relationtionship (Zappalà 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.
Highlights
The first sample return of an asteroid is planned in 2010.In September 2005, the Japanese spacecraft, Hayabusa, arrived at its near-Earth asteroid target, Itokawa, where it hovered above the surface of the asteroid until early December 2005
The physical characterization of asteroid Itokawa derived from our uniform multi-wavelength ground-based observations are very consistent with results from other groundbased campaigns as well as with the “ground-truth” found from in situ measurements by the Hayabusa spacecraft
Fine scale albedo and color variation seen by Hayabusa spacecraft (Saito et al, 2006) occur at too high a spatial resolution to be detected in any ground-based light curves
Summary
The first sample return of an asteroid is planned in 2010. In September 2005, the Japanese spacecraft, Hayabusa, arrived at its near-Earth asteroid target, Itokawa, where it hovered above the surface of the asteroid until early December 2005. We obtained 8 nights of BVRI broadband photometry data in January and February 2004 at Lowell Observatory as well as BVRI observations with the Magellan 6.5 meter telescopes in both January and June These data extend the solar phase angle coverage for the BVRI filters to a range from 4◦ out to 129◦. 2.1.1 Las Campanas Observatory The majority of the visible observations at LCO were made using the Swope 1 meter telescope (Bowen and Vaughan, 1973) and the Direct CCD Camera with a SITe detector This combination has a field of view of 14.8 × 22.8 and an image scale of 0.435 /pixel. The observations at Magellan were reduced in a similar fashion, via bias subtraction and flat fielding of all target and standard star frames followed by circular aperture photometry of all targets using IDL routines equivalent to the IRAF DAOphot packages. Calibration from instrumental magnitudes to standard magnitudes was performed through the observation of faint IR standards (Persson et al, 1998)
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