- Names
-
- M. Fastelli
- P. Comodi
- B. Schmitt
- P. Beck
- O. Poch
- P. Sassi
- A. Zucchini
- Title
- Reflectance spectra (1-5 µm) at low temperatures and different grain sizes of ammonium-bearing minerals relevant for icy bodies.
- Abstract
- It has been proposed that ammonium-bearing minerals are present in a varying amount in icy planetary bodies. Their observation at the surface of large objects was related to the upwelling and cryovolcanism of ammoniated water from possible subsurface oceans forming ammonium-bearing minerals ($NH_4^+$) mixed with ice at the surface. We analyzed the temperature evolution of the near-infrared spectra of a selected number of anhydrous and hydrated ammonium-bearing minerals containing different anions and water content. Reflectance spectra were collected in the 1-4.8 µm spectral range at cryogenic temperatures ranging from 293K to ~65K and the effect of sample’s grain size between 32 and 150 µm was also investigated at room temperature. Reflectance spectra of anhydrous samples show well-defined absorption bands in the 1-2.5 µm range. The bands located at ~ 1.06, 1.3, 1.56, 2.02, and 2.2 µm could be useful to discriminate these salts and their characteristics are examined in detail in this work. On the other hand, the reflectance spectra of water-rich samples show $H_2O$ fundamental absorption bands strongly overlapping the $NH_4^+$ bands, thus dominating the spectra from 1 to 2.8 μm and fully saturating above 2.8 μm. The position of the absorption bands changes with temperature and grain size, shifting to higher frequencies as temperature decreases. The low-temperature spectra also reveal a fine structure compared to the room temperature ones and display narrower and more defined absorption bands. Granulometry mainly affects the band depth and band area parameters. Moreover, mascagnite, salammoniac, ammonium phosphate, tschermigite, and ammonium nitrate are subjected to a reversible low-temperature phase transition, which is manifested in the spectra by a progressive growth and shift of the bands toward shorter wavelengths with an abrupt change in their depth. This new set of spectra at cryogenic temperatures can be directly compared with remote sensing data to detect the presence of ammonium-bearing minerals on the surface of icy bodies. Their identification can impact our knowledge of the internal composition and dynamics of these bodies as well as their potential habitability.
- Keywords
- spectroscopy, bidirectional reflection, bidirectional reflectance spectra, data analysis, near-IR, grain size, low temperature, phase change, band position, band width, band intensity, band integrated intensity, band vibration mode, mineral, Ammonium sulphate, mascagnite, Ammonium chloride, salammoniac, Larderellite, Struvite, Tschermigite, Ammonium carbonate, Ammonium phosphate monobasic, Ammonium nitrate, Ammonium bicarbonate, planet surface, Mars, polar cap
- Content
- sample, spectral data, band list data, planetary sciences
- Document type
- article
- Publication state
- published