Mineralogy of Ahuna Mons on Ceres surface

Kurzfassung

Ceres, the largest object in the main asteroid belt, and second target of the NASA Dawn mission, was mapped by VIR at different spatial resolutions. Visible and InfraRed (VIR) spectrometer onboard Dawn shed light on the overall surface composition of Ceres. The thermally-corrected average spectrum of Ceres as observed by VIR reveals the presence of several absorption bands in the 2.5 to 4 µm region (located at 2.7 µm, 3.1 µm, 3.3-3.4 µm, and 4 µm). The 2.7 µm band is diagnostic of hydrous minerals, the 3.1 µm band is associated with NH4-phyllosilicates, while both the 3.3-3.4 and the 4 µm bands are typical of the carbonates signature (De Sanctis et al., 2015). The first spatial resolved map of Ceres obtained on the basis of Dawn optical imagery revealed an overall dark surface with widespread albedo variations (Nathues et al., 2015). Ahuna Mons is an isolated elliptical mountain (21x13 km) located at 10.48°S, 316.2°E, and it has peculiar morphological characteristics. It is surrounded by a smooth-textured unit, less cratered than nearby terrains, and it can divided in two units: a summit with sub-radial arcuate structures (ridges and troughs) and a steep flanks formed by talus material (Ruesch et al., 2016). Ahuna Mons was formed by a volcanic process involving ascent of cryomagma and extrusion onto the surface followed by dome development (ibid). Spectroscopic analysis carried out in the Ahuna Mons region on the basis of VIR data indicates that this geological unit stands out as being distinct from the surrounding regions with respect to a series of diagnostic spectral indicators. Although the overall composition is not dissimilar from what is found elsewhere on Ceres, at the local scale Ahuna Mons emerges to have a lower abundance of hydrous mineral phases and a greater abundance of Na-carbonates than the surrounding areas observed at the same spatial resolution. The presence of a large amount of Na-carbonates is also consistent with the composition of the Occator bright spot (De Sanctis et al., 2016). This evidence is ultimately consistent with a cryovolcanic origin of Ahuna Mons, which would locally raise a portion of terrain by exposing fresh subsurface material richer in carbonates.