High‐Temperature VIS‐IR Spectroscopy of NH₄‐Phyllosilicates

Abstract

The presence of ammonium-bearing minerals on the surface of (1) Ceres has been first suggested by King et al. (1992), using ground-based spectral data. After that, NH 4 -phyllosilicates have been advocated as one of the main constituents of the Ceres surface (Ammannito et al., 2016;, interpreting to the spectra acquired by the VIR spectrometer (De Sanctis, Coradini, et al., 2011) onboard the Dawn spacecraft (C. T. Russell et al., 2004). The Ceres spectra in the range of 1-5 μm have shown a clear signature at 3.06-3.07 μm, assigned to NH 4 -phyllosilicate. Nevertheless, the specific phyllosilicates bearing ammonium were not fully constrained, also due to the limited availability of NH 4 + -phyllosilicate spectra acquired in the laboratories (

Laboratory Investigations Coupled to VIR/Dawn Observations to Quantify the Large Concentrations of Organic Matter on Ceres

“…Additionally, possible water absorption was not controlled on our analogues; they have been manipulated under ambient temperature and air, while measurements were done under nitrogen flux. A small quantity of absorbed water can hence broaden the 3 µm band, as observed for ammonium-phyllosilicates [31], and indeed noted on our spectra. This band profile is barely observed on the Ceres spectra.…”

Organic Matter and Associated Minerals on the Dwarf Planet Ceres

“…However, the spectra of these chondrites are not a perfect match with Ceres at other wavelengths and, even if the average spectrum of Ceres is broadly similar to that of CM chondrites, specific spectral bands indicate variations in the mineral mixture composing the surface. The most remarkable difference is that CM and CI chondrites lack Ceres' features at 3.05-3.1 µm (Figure 2b), attributed to the presence of NH4 in the phyllosilicates [23,35], as demonstrated by spectral measurements on ammoniated-phyllosilicates in laboratory [27,[36][37][38]. Ammoniated clays have not been identified in carbonaceous chondrites, but NH 3 is a component of organics in CM/CI chondrites [39].…”

“…As a consequence, including carbonaceous-chondrites as the main component of the Ceres-like mixture implies an even more abundant quantity of carbon and organics as described by [17]. Some attempts in reproducing the average spectrum of Ceres in the laboratory have been made [27] using mixtures of phyllosilicates, with and without ammonium, carbonates and dark phases. The results suggest that the mixtures are able to reproduce the average spectrum of Ceres, even if some minor discrepancies are still to be solved.…”

Reflectance spectra of mascagnite and salammoniac minerals with varying viewing geometry

“…Up to now, several laboratory studies have analysed in detail ammonium bearing minerals using visible and near-infrared spectroscopy at various temperatures and considering different particle sizes (e.g., (Berg et al, 2016;Ciarniello et al, 2017;De Angelis et al, 2021a;Ehlmann et al, 2018;Fastelli et al, 2020;Krohn and Altaner, 1987). In all these works, the variation in viewing geometry has not been examined for the here reported samples.…”