Volatiles on Mercury: The case of hollows and the pyroclastic vent of Tyagaraja crater

The direct evidence of volatile elements in Mercury's interior and on its surface is testified by the presence of pyroclastic vents and hollows, respectively, that in some locations could co-occur. For this reason, in this study we analyze the Tyagaraja impact crater to give new insights into the nature of the hollows located on its floor as well as on the pyroclastic vent and associated deposits. By means of MDIS images, we performed a high-resolution geological map to describe the Tyagaraja's geological setting and distinguish its different geological units. Then, we apply a spectral clustering technique able to separate the dataset in different clusters, each one characterized by its spectrum. Through the comparison between the geomorphological and spectrophotometric results we find that the hollows and the pyroclastic deposit in Tyagaraja are characterized by different spectra. Hollows have the bluest spectrum, with a prominent absorption band at 0.63 μm, in addition to a possible combination of bands (or a single broadband) centered at 0.75 μm and 0.83 μm. On the contrary, the pyroclastic deposit presents the reddest spectrum, characterized by a convex curvature. After considering several volatiles candidate minerals and by applying a linear spectral mixing, we find that the composition of the pyroclastic deposit is well described by a combination of sulfides minerals, in agreement with previous results. On the other hand, hollows may be represented by a combination of chloride minerals. This supports the hypothesis that a localized hollows-forming volatile layer enriched in chlorides might have been generated during the differentiation of the impact melts infilling the crater floor. Such results suggest that the volatile material responsible for hollows formation may be different from the volatiles of pyroclastic eruptions and change depending on the location of the hollows in the hosting impact crater. •High resolution geological map of Tyagaraja crater hosting both hollows and pyroclastic deposit•Tyagaraja pyroclastic deposit well described by a combination of sulfides minerals.•Tyagaraja hollows represented by a combination of chlorides minerals.•Localized hollows-forming volatile layer formed during the differentiation of the impact melts.•Volatile material responsible for hollows formation depends on hosting impact crater's location.