20-EPN-029: Vis-NIR reflection spectroscopy of ammonium salts relevant for icy planetary surface characterisation
Virtual visit by Maximiliano Fastelli, University of Perugia (Italy), to TA2.8 CSS (Cold Surfaces Spectroscopy) at IPAG (France).
Dates of visit: 13 October – 5 November 2021
Report Summary: During this TA visit under Europlanet 2024 RI 2nd call, reflectance VIS-NIR spectra of several ammonium salts were collected at the CSS facility (IPAG laboratory) in Grenoble, France. Different temperature steps were chosen to collect cryogenic data down to 90 K. Samples were characterised by low temperature crystalline phase transitions, and for these reasons, the measurement steps have been increased in the proximity of the expected temperature of mineral transformation. Cooling and heating experiments, using the same cooling/heating rate, were performed to bracket the phase transition T and verify its reversibility. All the spectra were collected with three different grain size (150/125 – 125/80 – 80/32 μm) in the spectral range from 1 to 4.6 μm at low T. Typical absorption features due to overtones and combinations of NH4+ groups were identified in the spectral range investigated. Phase transitions, when detected, show an interesting behaviour with change in shape and position of some (sensitive) absorption bands which could be useful for the identification of these phases at non-ambient T. Moreover, the effect of low T and different granulometry were observed.
It has been proposed that ammonium minerals are present in varying percentages in icy planetary bodies. The availability of these compounds is linked to the upwelling of ammonium salts (NH4+) with ice from the subsurface of possible oceans resulting from cryovolcanism phenomena. The identification of these minerals on the surface can give information about internal composition/dynamics and potential habitability of icy bodies.
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