Detection of a novel spectral feature at 830 nm in MDIS/MESSENGER color image of Praxiteles basin

Kurzfassung

Hollows, flat-floored depressions with bright edges, are peculiar spectral units on the surface of Mercury [1,2], the only ones where an absorption band at 630 nm was detected in MDIS/MESSENGER multicolor images. The feature was observed in hollows of Dominici and Hopper craters, extending from 559 to 828 nm in hollows of Canova and Velazquez craters, mainly ascribed to sulphides and chlorides [4,6], although additional components could occur, such as transitional elements, different from iron, on pyroxenes. Additionally, hollows have flatter MDIS spectra, a strong curvature shortward of 600 nm and the highest UV downturn shortward of 400 nm [8,9] in MASCS spectra. We spectrally analysed the Praxiteles basin (198 km in diameter), hosting hollows, faculae and low-reflectance material (LRM), the supposed parent material of hollows. The floor is covered by low-reflectance blue plains (LBP) likely produced by effusive volcanism. We detected a reflectance minimum at 828.4 nm in several MDIS spectra within the basin, suggesting the existence of a novel absorption band. Spectral examination and geological inspection of MDIS data link the absorption band to relatively fresh material exposed through hollows formation and/or mass wasting.