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Volcanic products are widely present on Mercury: they occur as low-viscosity lava flows, but traces of ash deriving from explosive volcanism are also observed. Silicate glasses represent a major component in volcanic products, and it is likely that the fine-powdered regolith on Mercury contains a non-negligible fraction of glassy material. In the laboratory, we have reproduced a Mercury-like silicate glass, from which we have obtained 14 powdered samples with different granulometric characteristics: 8 samples are extremely sorted with grain sizes ranging from 25 to 425 µm, and 6 samples consist of less sorted powders with normal distributions, varying mean values (30, 95, and 160 µm) and standard deviation (40 and 80 µm). The reflectance of samples was investigated in the mid-infrared (MIR) region: we observe how the reflectance intensity increases with grain size, and the presence of extremely fine material defines the emergence of the transparency feature (TF). We provide reference data with qualitative observations and quantitative parameterization of spectral characteristics; in particular, we observe how a small fraction of fine material can greatly influence the spectral response of coarser powders. Results of this work will be crucial for the interpretation of data collected by the BepiColombo mission, but need to be integrated with other possible Mercurian compositions. [ABSTRACT FROM AUTHOR]

A correction to the article "Formation of Molecular Oxygen and Ozone on Amorphous Silicates" that was published in the 2012, 756, 98 issue is presented.

Oxygen in the interstellar medium is seen in the gas phase, in ices (incorporated in H2O, CO, and CO2), and in grains such as (MgxFe1–x)SiO3 or (MgxFe1–x)2SiO4, 0 < x < 1. In this investigation, we study the diffusion of oxygen atoms and the formation of oxygen molecules and ozone on the surface of an amorphous silicate film. We find that ozone is formed at low temperature (<30 K), and molecular oxygen forms when the diffusion of oxygen atoms becomes significant, at around 60 K. This experiment, besides being the first determination of the diffusion energy barrier (1785 ± 35 K) for oxygen atoms on a silicate surface, suggests bare silicates as a possible storage place for oxygen atoms in low-Av environments. [ABSTRACT FROM AUTHOR]