Correlations and Relations Between Galileo NIMS and SSI Measurements for Callisto

C.A. Hibbitts, T.B. McCord, G.B. Hansen (HIGP/SOEST Univ. of Hawaii), J. Klemaszewski, R. Greeley, K.C. Bender (Arizona State Univ.), M. Segura, R.W. Carlson, W.D. Smythe (Jet Propulsion Lab.), G. Neukum, T. Denk (DLR, Inst. for Planet. Expl.), P. Geissler (LPL, Univ. of Arizona), M.J.S. Belton (NOAO, Tucson, AZ)

Precisely registered SSI and NIMS observations of Callisto reveal correlations between spectral properties and structural, morphological, and albedo features. The spectral features discovered by NIMS which are strong enough to be mapped include absorption bands near 3.88, 4.05, 4.25 and 4.57 m (1). These features are also consistent between regional and global images demonstrating self-consistency in the NIMS observations (2). Projections of the NIMS maps of 1.48 m absorption band depth, which is related to water-ice concentration and free of many photometric irregularities, were registered to bright albedo features within similar projections of the SSI observations. Minor rubber-stretching removed the effects of small positional uncertainties. This more rigorous approach to looking for correlations between the observations has confirmed our initial findings (3) and much more accurately determined relations between topography and probable volatile concentrations. The SSI blue spectral unit still correlates well, but not perfectly, with the depth of the NIMS 1.48 5m band strengths implying that the blue color may not be entirely due to the presence of more water ice. The 4.25 m absorption band's relation to morphology, obviously strong at both Burr and Tornusuk craters, has been much more accurately determined. Similar results have been achieved with the 4.05 m absorption band, which has previously only been shown to be absent from the center of the Asgard Basin and generally stronger in the southern hemisphere, as well as with the 3.88 and 4.57 m absorption bands.

(1) McCord et al., 1997, Science, submitted; McCord et al., 1997, EGS and AGU, (abstracts). (2) McCord et al., 1997, JGR, (submitted). (3) McCord et al., 1997, AGU, (abstract).