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The remnants of explosive volcanism on Mercury have been observed in the form of vents and pyroclastic deposits, termed faculae, using data from the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) onboard the Mercury surface, space environment, geochemistry, and ranging (MESSENGER) spacecraft. Although these features present a wide variety of sizes, shapes, and spectral properties, the large number of observations and the lack of high-resolution hyperspectral images complicates their detailed characterisation. We investigate the application of unsupervised deep learning to explore the diversity and constrain the extent of the Hermean pyroclastic deposits. We use a three-dimensional convolutional autoencoder (3DCAE) to extract the spectral and spatial attributes that characterise these features and to create cluster maps constructing a unique framework to compare different deposits. From the cluster maps we define the boundaries of 55 irregular deposits covering 110 vents and compare the results with previous radius and surface estimates. We find that the network is capable of extracting spatial information such as the border of the faculae, and spectral information to altogether highlight the pyroclastic deposits from the background terrain. Overall, we find the 3DCAE an effective technique to analyse sparse observations in planetary sciences. [ABSTRACT FROM AUTHOR]

Mercury's peculiar orbit around the Sun (3:2 spin–orbit resonance) and lack of atmosphere result in one the widest temperature ranges experienced at the surface of a planetary body in the solar system. Temperature variations affect the physical and, therefore, spectral properties of minerals to varying degrees; thus, it is crucial to study them in the context of the upcoming arrival of the BepiColombo spacecraft in Mercury orbit in the fall of 2025. In this work, we heated and cooled analog materials (plagioclase and volcanic glasses) at temperatures representative of the hermean surface. With our experimental setup, we could measure near-infrared (1.0–3.5 μ m) and thermal infrared (2.0–14.3 μ m) reflectance spectra of our analogs at various temperatures during a heating (25–400 ∘ C) or cooling cycle (−125–25 ∘ C), allowing us to follow the evolution of the spectral properties of minerals. We also collected reflectance spectra in the visible domain (0.47–14.3 μ m) before and after heating. In the visible spectra, we identified irreversible changes in the spectral slope (reddening) and the reflectance (darkening or brightening) that are possibly associated with oxidation, whereas the temperature had reversible effects (e.g., band shifts of from ten to a hundred nanometers towards greater wavelengths) on the infrared spectral features of our samples. These reversible changes are likely caused by the crystal lattice dilatation during heating. Finally, we took advantage of the water and ice present on/in our samples to study the different components of the absorption band at 3.0 μ m when varying temperatures, which may be useful as a complement to future observations of the north pole of Mercury. The wavelength ranges covered by our measurements are of interest for the SIMBIO-SYS and MERTIS instruments, which will map the mineralogy of Mercury's surface from spring 2026, and for which we selected useful spectral parameters that are proxies of surface temperature variations. [ABSTRACT FROM AUTHOR]

Abstract: Mercury’s sodium exosphere has been observed only few times with high spectral resolution from ground based observatories enabling the analysis of the emission spectra. These observations highlighted the energetic state of the sodium exospheric atoms relative to the surface temperature. More recently, the Doppler shift of the exospheric Na atoms was measured and interpreted as consistent with an exosphere moving outwards from the subsolar point (Potter, A.E., Morgan, T.H., Killen, R.E. [2009]. Icarus 204, 355–367). Using THEMIS solar telescope, we observed Mercury’s sodium exosphere with very high spectral resolution at two opposite positions of its orbit. Using this very high spectral resolution and the scanning capabilities of THEMIS, we were able to reconstruct the 2D spatial distributions of the Doppler shifts and widths of the sodium atomic Na D 2 and D 1 lines. These observations revealed surprisingly large Doppler shift as well as spectral width consistent with previous observations. Starting from our 3D model of Mercury Na exosphere (Mercury Exosphere Global Circulation Model, Leblanc, F., Johnson, R.E. [2010]. Icarus 209, 280–300), we coupled this model with a 3D radiative transfer model described in a companion paper (Chaufray, J.Y., Leblanc, F. [2013]. Icarus, submitted for publication) which allows us to properly treat the non-maxwellian state of the simulated sodium exospheric population. Comparisons between THEMIS observations and simulations suggest that the previously observed energetic state of the Na exosphere might be essentially explained by a state of the Na exospheric atoms far from thermal equilibrium along with the Doppler shift dispersion of the Na atoms induced by the solar radiation pressure. However, the Doppler shift of the spectral lines cannot be explained by our modelling, suggesting either an exosphere spatially structured very differently than in our model or the inaccuracy of the spectral calibration when deriving the Doppler shift. [Copyright &y& Elsevier]

The understanding of volcanic explosive episodes on the surface of Mercury has important implications for the origin, history and inventory of Mercury's volatiles and for the thermal evolution of the planet. The hermean explosive features are pits, interpreted as endogenic pyroclastic vents often surrounded by bright and diffuse deposits, named faculae, and interpreted as pyroclastic material. We present a global spectroscopic survey of the surroundings of the listed endogenous pits, derived from spectra obtained by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS/MESSENGER). The spectral properties of 26 faculae around endogenous pits were characterized. The diameter of 80% of them has been reassessed upwards by 17 km on average, implying volatile contents needed to emplace these deposits consequently higher than estimated in previous studies. These observations suggest a higher bulk volatile content or subsurface volatile enhancement. Spectral similarities between faculae located in the same crater indicate either a similar magmatic source or a large fraction of country rocks. The size, volatile content, location, and spectral properties of Nathair Facula seem to indicate an anomaly with respect to the other faculae that may be explained by a phreatomagmatic-like event by interaction between hot-magma and local carbon-rich layer • The dimensions of the faculae seem to have been underestimated by on average 17 km. • Spectral properties of nearby faculae suggest either a similar magmatic origin or large fractions of country rocks. • Physical and spectral properties of Nathair Facula suggest emplacement by a phreatomagmatic-like process. [ABSTRACT FROM AUTHOR]

\begin{document}MErcury Surface, Space ENvironnement, GEochemistry and Ranging (MESSENGER) mission made possible to highlight, in part, explosive volcanism on the surface of Mercury. Witnesses of this volcanic activity are irregularly shape depressions surrounded by bright deposits named pyroclastic deposits [1]. Spectrally, deposits appear brighter and redder than Mercury background [2]. Spectral properties, in some deposits on the edges of the Caloris bassin, vary across the deposit [3]. We investigate the evolution of several spectral parameters with the distance to the vent for pyroclastic deposits in various locations/regions on the Hermean surface. Because of the importance of this characteristic for understanding the interior volatile abundance of Mercury, we spectrally determine the radius of these deposits which are greater in many cases than the radius estimated previously by visual analyses [4]. Spectral parameters can be used, also, to determine geomorphology of the deposits, and constrain eruptive history. In this study, we focus on two morphologically different deposits: NE Rachmaninoff and RS-03 in Caloris [5] and we deduce two different eruptive histories on Mercury. \begin{thebibliography}{} \bibitem[1]{2008Head} Head J.W, et al. (2008), Science, 321, 69-72 \bibitem[2]{2009Kerber} Kerber L, et al. (2009), Earth and Planetary Science Letters, 285, 263-271 \bibitem[3]{2015Besse} Besse S, et al. (2015), Journal of Geophysical Research: Planets, 120 \bibitem[4]{2011Kerber} Kerber L, et al. (2011), Planetary and Space Science, 59, 1895-1909 \bibitem[5]{2014Rothery} Rothery D.A, et al. (2014), Earth and Planetary Science Letters, 385,59-67\end{thebibliography}\end{document} [ABSTRACT FROM AUTHOR]

\begin{document}A major result of the MESSENGER mission was to reveal the volcanic hermean surface poor in iron [Peplowski et al., 2016], but unexpectedly rich in volatile elements [Nittler et al., 2011]. The high abundance of sulfur on Mercury is particularly interesting, because its sublimation is suggested to trigger the formation of hollows [Blewett et al., 2013]. Laboratory experiments whose aim is to study the evolution of sulfides in the conditions of Mercury's surface are in progress [Varatharajan et al., 2018]. However, to understand the spectral properties of the surface, it is relevant to consider how minerals can be affected by the hermean environment. The effects of temperature and space weathering on minerals have been already studied [e.g. Suto et al., 2006; Helbert et al., 2013; Brunetto et al., 2014] but rarely on retrieved Mercury\textsc{\char13}s composition analogs [Morlok et al., 2017]. Here we focus on the effects on minerals analogs of the extreme variations of temperature occurring on Mercury. \\We preliminarly consider a plagioclase An80 [Serventi et al., 2014] as a Mercury's minerals analogs under different states (powder, pellet and slice). Other analogs are about to be tested (e.g. ion-irradiated forsterite and nepheline half covered with a thin film of carbon [Carli et al., 2018]). To simulate the hermean temperature conditions (80-700 K), we used a LINKAM (nitrogen purged) cell to heat and cool our samples which allows to measure VIS-IR (0.4-15 $\mu$m) spectra as a function of temperature. We have two setups for our spectroscopic measurements: 1) a visible-near infrared spectrometer Maya2000 Pro coupled with a microscope through optical fibers; 2) a near to mid infrared spectrometer coupled with an Agilent microscope, installed at the SMIS (Spectroscopy and Microscopy in the Infrared using Synchrotron) beamline of the synchrotron SOLEIL. \\An ongoing analysis for the plagioclase samples showed: 1) a darkening of the samples when increasing T; 2) a shift towards greater wavelengths for the Christiansen feature and several Reststrahlen bands (RB) (e.g. at $\sim$9.0 and $\sim$10.5 $\mu$m) as a function of increasing T; 3) a decreasing of the bands depth when increasing T; 4) a shape changing for some RB; 5) a monotonous spectral slope variation with increasing T. Most of these spectral variabilities are in agreement with studies on the emissivity of the other minerals (e.g. [Helbert et al., 2013b]) and are similar to those of the space weathering [Brunetto et al., 2015], except the fact that they are reversible. A more complete analysis will be presented. \\Acknowledgements: This work is partly supported by the Centre National d\textsc{\char13}\'Etudes Spatiales. The microspectroscopy activities are supported by grants from R\'egion Ile-de-France (DIM-ACAV) and SOLEIL. D. Perna received funding from the European Union's Horizon 2020 research \& innovation program under the Marie Sklodowska-Curie grant agreement n.664931.\end{document} [ABSTRACT FROM AUTHOR]