MINERALOGICAL ANALYSIS OF THE HAULANI QUADRANGLE ON THE DWARF PLANET CERES

Abstract

Quadrangle 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 high albedo (bright) ejecta that extend around crater Haulani, which gives the name to the quadrangle. In Dawn’s Framing Camera (FC) color-ratio composite images, crater Haulani is clearly distinct compared to surrounding terrains. Haulani’s bright material displays a very small or even negative (blue) spectral slope in the range from the visible to the near infrared, which is a peculiar occurrence compared to rest of the quadrangle and more generally to the average surface of Ceres. Hyperspectral images returned by the Visible and InfraRed (VIR) mapping spectrometer onboard Dawn enabled a careful mineralogical analysis of the Haulani quadrangle. In the High-Altitude Mapping Orbit HAMO phase, yielding an average pixel resolution of ~0.38 km, VIR obtained nearly global coverage of quadrangle Ac-H-6. Based on this dataset, crater Haulani also stands out compared to the rest of the quadrangle. The spectral features centered at 2.7 and 3.06 µm, respectively indicative of the presence of hydrous minerals and ammoniated phyllosilicates, show a decrease of band depth in the floor and in Haulani’s bright ejecta, corresponding to the blue spectral slope. Similar, but less prominent, spectral behavior, is observed in other small craters found within this quadrangle.