Mineralogical Analysis of the Haulani Quadrangle of the Dwarf Planet Ceres

1F.Tosi et al.
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.08.012]
1INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy
Copyright Elsevier

Ac-H-6 ‘Haulani’ is one of five quadrangles that cover the equatorial region of the dwarf planet Ceres. This quadrangle is notable for the broad, spectrally distinct ejecta that originate from the crater Haulani, which gives the name to the quadrangle. These ejecta exhibit one of the most negative (‘bluest’) visible to near infrared spectral slope observed across the entire body and have distinct color properties as seen in multispectral composite images. Besides Haulani, here we investigate a broader area that includes other surface features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features.

Our analysis shows that crater Haulani stands out compared to other surface features of the quadrangle. Albedo maps obtained in the near infrared range at 1.2 μm and 1.9 μm reveal that the floor and ejecta of Haulani are indeed a patchwork of bright and dark material units. Visible to near-infrared spectral slopes display negative values in crater Haulani’s floor and ejecta, which are indicative of a younger age. Spectral features centered at ∼2.7 μm and ∼3.1 μm, respectively diagnostic of magnesium-bearing phyllosilicates and ammoniated phyllosilicates, show a substantial decrease in band depth in crater Haulani’s floor and bright ejecta. Similar, but less prominent, spectral behavior is observed in other small craters of this quadrangle. There is a general trend in quadrangle Ac-H-6 for the two 2.7-μm and 3.1-μm band depths to increase from the northwest to the southeast. However, it is worth noting that the correlation between these two spectral parameters is generally strong in the Haulani crater’s area, but much weaker elsewhere, which indicates a variable degree of mixing between these two major mineral phases.

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