Mercury Hollows as Remnants of Original Bedrock Materials and Devolatilization Processes: A Spectral Clustering and Geomorphological Analysis

We perform a detailed geomorphological and compositional analysis on three craters hosting hollows located in the Victoria and Kuiper Quadrangles of Mercury. Based on Mercury Dual Imaging System data, high-resolution detailed geomorphological mapping is provided in order to fully characterize the geological framework where hollows formed. In addition, we apply an unsupervised spectral clustering, based on a K-mean algorithm, to separate in clusters our data sets. The comparison between the spectral and the well-defined geomorphological units reveals a spatially coherent distribution. In particular, all hollows are uniquely identified by a well-defined spectrum showing a wide absorption band between 0.558 and 0.828, with a possible hint of absorption toward 1 \u3bcm. Our analysis suggests that the composition of hollows may be characterized by a mixture of different minerals contributing to the absorptions found in our spectra. Indeed, sulfides alone (CaS, MnS, and MgS) cannot explain the spectrum behavior of hollows, even if the mechanism forming hollows likely involves the loss of volatiles from the surface. Hence, we have to consider bedrock-forming material as partial responsible of the absorptions. For the studied hollows we suggest that the bedrock-forming minerals are pyroxenes presenting transitional elements, like Cr, Ti, and Ni in substitution of Mg and/or Fe. Therefore, we suggest that the spectral characteristics of hollows are related to both remnant material produced by devolatilization process and to bedrock in which the hollows formed