36th DPS Meeting, 8-12 November 2004
Session 32 Asteroids
Poster II, Thursday, November 11, 2004, 4:15-7:00pm, Exhibition Hall 1A

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[32.09] Improved NASA Infrared Telescope Facility (IRTF) Spectral Reduction Procedures and Compositional Results of Asteroid 25143 Itokawa

K. S. Jarvis (Lockheed Martin Space Operations), P. A. Abell, F. Vilas (NASA-JSC), M. J. Gaffey (Univ. of North Dakota), M. S. Kelley (Georgia Southern Univ)

The Japanese Hayabusa (MUSES-C) spacecraft, launched in 2003, is slated to encounter asteroid 25143 Itokawa in the fall of 2005. The spacecraft will obtain spectra from 0.85 – 2.1 microns, and return samples of the asteroid to Earth. A ground-based observing program to obtain comprehensive spectral data of this asteroid has been underway since the selection of Itokawa as the Hayabusa target. At the Lunar and Planetary Science Conference 2004, initial results of several nights of spectral data taken at the NASA IRTF in March 2001 were displayed. This data have since been reprocessed using a combination of data reduction techniques utilized by the Planetary Astronomy Group at JSC-NASA and by the Asteroid Studies Group at the University of North Dakota. We report the results of the newly re-processed data and the accompanying techniques, with the previously processed data shown for comparison. The compositional results from the reprocessed data will be reported and correlated to the rotational phase of the asteroid at the time the observations were obtained. In addition, a comparison of the compositional information using spectra from both the current and previous methods used for the analysis will be presented.

Analyses of the data obtained suggest that Itokawa’s surface is composed of an olivine and orthopyroxene mineralogy. The band positions of the absorption features located near 1 and 2 microns suggest that the mean pyroxene chemistry is ~ Wo7-17Fs39. There appear to be two pyroxene components, primarily a low-Ca orthopyroxene with a significant additional Ca-pyroxene phase. These pyroxene compositions are suggestive of phases crystallized from partial melts, which indicates that the parent body of 25143 Itokawa reached temperatures sufficient to initiate partial melting, but it did not attain the degree of melting required for significant melt mobilization. Hence Itokawa appears to be analogous to a primitive achondrite.

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