20-EPN-042: Reflectance spectroscopy of ammonium-bearing minerals
September 5, 2021

20-EPN-042: Reflectance spectroscopy of ammonium-bearing minerals – A tool to improve the knowledge of the surface of icy planetary bodies.

Virtual visit by Maximiliano Fastelli, University of Perugia (Italy), to TA2.8 CSS (Cold Surfaces Spectroscopy) at IPAG (France).
Dates of visit: 09-27 November 2020

Report Summary: In the frame of the Europlanet 2024 1st TA call, reflectance VIS-NIR spectra were collected. Ten different temperature steps were chosen to collect cryogenic data: 270-245-220-180-160-140-120-100-90-270 up K.

For the samples characterized by a low temperature phase transitions (mascagnite (NH4)2SO4, sal-ammoniac NH4Cl, ammonium phosphate (NH4)H2PO4, tschermigite (NH4)Al(SO4)2·12(H2O) and ammonium nitrate NH4NO3), 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 break the phase transition T. In particular, mascagnite, sal-amoniac and ammonium phosphate monobasic samples showed clear and very interesting spectral bands variations during cooling, indicating that a phase transition occurred. Spectra were collected with three different grain size (150/125 – 125/80 – 80/32 μm) in the spectral range from 1 to 4.8 μm. 

The collected data will help on the interpretation of VIR remote spectra from Europa, Pluto’s moons, Enceladus and other icy celestial bodies surface where NH4 minerals have been supposed to occur. Moreover, the study of ammonium bearing minerals and their behavior at very low temperature might give information on how the phase transition affects the bands position and shapes inside the reflectance spectra. Overtones and combinations of NH4 bands are in the 1-3 μm range, whereas fundamental vibrational modes (ν1 and ν3) are present in the ~3 μm area.