Other
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.1103h&link_type=abstract
American Astronomical Society, DPS meeting #39, #11.03; Bulletin of the American Astronomical Society, Vol. 39, p.428
Other
Scientific paper
Hydrated nonice material is ubiquitous on Ganymede [1]. Another non-ice material, associated with dark rays exists which may be due to impactor contamination [2,3]. Work using only a few NIMS observations showed that dark rays contain a less hydrated material spectrally similar to a C-type asteroid or to nonice material on Callisto [4].
We expand upon this work using all NIMS observations of dark rays and many other NIMS observations. Because every pixel of every NIMS observation contains effects of water-ice, we first derive the residual nonice material in each observation by removing (assuming areal mixing) the bi-directional reflectance of water-ice from the least icy spectrum. We then reproduced the spectrum of ganymede hydrate [1], derived the spectra of dark rays, and the spectra of other dark material.
The spectra of dark rays are consistent with the presence of ganymede hydrate and several 10s % (areal mixture) of a single less hydrated material spectrally consistent with previous results. This second nonice material reduces the depth of the 1.5- and 2-um water-related bands and the contrast of the broad 3-um OH-related band. Kittu ejecta contains the greatest fraction of dessicated material, but is otherwise spectrally identical to other dark ray craters. Spectra of non-ray dark material are consistent with Ganymede hydrate, though a small amount (<10%) of dessicated material could be present. The correlation of the less-hydrated material with dark rays is consitent with impactor contamination but dessication of ganymede hydrate during impact may also be an explanation.
Acknowlegements: This work has been supported by internal APL funds (Janney) and NASA OPR Grant NNX0GAD15G.
References: [1] McCord et al., Science, 292, 1523-1525, 2001. [2] Conca et al., LPSC XII, 172-174, 1981. [3] Schenk, P. and W.B. McKinnon, Icarus, 89, 318-346, 1991. [4] Hibbitts et al., Bull. Amer. Astron. Soc., EAE03-A-07806, 2003.
Hansen Gary B.
Hibbitts Charles A.
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