Ambient and cold-temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies

Mg‐phyllosilicate‐bearing, dark surface materials on the dwarf planet Ceres have NH_4‐bearing materials, indicated by a distinctive 3.06 μm absorption feature. To constrain the identity of the Ceres NH_4‐carrier phase(s), we ammoniated ground particulates of candidate materials to compare their spectral properties to infrared data acquired by Dawn's Visible and Infrared (VIR) imaging spectrometer. We treated Mg‐, Fe‐, and Al‐smectite clay minerals; Mg‐serpentines; Mg‐chlorite; and a suite of carbonaceous meteorites with NH_4‐acetate to exchange ammonium. Serpentines and chlorites showed no evidence for ammoniation, as expected due to their lack of exchangeable interlayer sites. Most smectites showed evidence for ammoniation by incorporation of NH_4^+ into their interlayers, resulting in the appearance of absorptions from 3.02 to 3.08 μm. Meteorite samples tested had weak absorptions between 3.0 and 3.1 μm but showed little clear evidence for enhancement upon ammoniation, likely due to the high proportion of serpentine and other minerals relative to expandable smectite phases or to NH_4^+ complexing with organics or other constituents. The wavelength position of the smectite NH4 absorption showed no variation between IR spectra acquired under dry‐air purge at 25 °C and under vacuum at 25 °C to −180 °C. Collectively, data from the smectite samples show that the precise center wavelength of the characteristic ~3.05 μm v_3 absorption in NH_4 is variable and is likely related to the degree of hydrogen bonding of NH_4‐H_2O complexes. Comparison with Dawn VIR spectra indicates that the hypothesis of Mg‐saponite as the ammonium carrier phase is the simplest explanation for observed data, and that Ceres dark materials may be like Cold Bokkeveld or Tagish Lake but with proportionally more Mg‐smectite

Laboratory experiments on ammoniated clay minerals with relevance for asteroid (1) Ceres

Recent observations with VIR spectrometer onboard Dawn spacecraft [1] have suggested the presence of ammoniated phyllosilicates widespread on the surface of asteroid (1) Ceres [2,3]. The global surface composition of Ceres as suggested by VIR average infrared spectrum in the 1-4 micron range appears to be due to a mixture of NH4-bearing phyllosilicates, serpentine, carbonates and a dark absorbing phase (magnetite or amorphous carbon) [2]. An absorption feature occurring near 3.1 micron in the average spectrum is considered the main evidence for the presence of NH4-bearing phase; nevertheless in the past several authors tried to explain this feature, as observed with telescopic spectra, invoking the presence of brucite, cronstedtite, water ice or clays [4]. In this project we are carrying out laboratory experiments with the aim of studying ammoniated phyllosilicates in the visible-infrared range. A suite of 9 clay minerals has been used for this study, including illite, nontronite and montmorillonite. In order to produce the ammoniated species we followed a modified procedure based on the one described in Bishop et al. (2002) [5]. All minerals were reduced in fine grain size (<36 micron), treated with ammonium hydroxide (NH4OH) and heated in oven at 200°C for 24 h at normal pressure conditions, before the measurements. Reflectance spectra were acquired with the Fourier Transform Infrared Spectrometer (FTIR) in use at INAF-IAPS/P-LAB, in the range 1-14 μm, on both clay minerals and NH4-treated clays. Almost all spectra of NH4-treated species are characterized by the occurrence of several new absorption features, appearing at different wavelengths near 2, 3, 6 and 7 micron. In some cases the spectral shape of already existent absorption bands resulted deeply modified. A few species did not show the appearance of new features. These results suggest that NH4+ ions fix in various ways in different minerals. Nontronite and montmorillonite appear to be the best candidates, among the studied suite, to be used in future laboratory reproduced analog mixtures. [1] Russell C.T. et al., 2004, Planetary and Space Science, 52, 465-489 [2] De Sanctis M.C. et al., 2015, Nature, 528, 241-244 [3] Ammannito E. et al., 2016, Science, vol.353, issue 6303 [4] Rivkin A.S. et al., 2011, Space Science Reviews, 163, 95-116 [5] Bishop J.L. et al., 2002, Planetary and Space Science, 50, 11-1

The Ma_Miss instrument performance, II: Band parameters of rocks powders spectra by Martian VNIR spectrometer

We wish to thank the Italian Space Agency (ASI) for funding and fully supporting the Ma_Miss experiment (ASI/INAF grant I/ 060/10/0). We also thank G.F. De Astis (INGV) for providing the Aeolian samples, and A.Frigeri for providing the red micritic limestone. We thank an anonymous reviewer for useful comments and suggestions.The Ma_Miss instrument (Mars Multispectral Imager for Subsurface Studies, Coradini et al. (2001)) is a Visible and Near Infrared miniaturized spectrometer that will observe the Martian subsurface in the 0.4-2.2 μm spectral range. The instrument will be entirely hosted within the Drill of the ExoMars-2018 Pasteur Rover: it will allow analyzing the borehole wall excavated by the Drill, at different depths, down to 2 m. The aim will be to investigate and characterize the mineralogy and stratigraphy of the shallow Martian subsurface. A series of spectroscopic measurements have been performed in order to characterize the spectral performances of the laboratory model of the instrument (breadboard). A set of six samples have been analyzed. Each sample (four volcanic rocks, a micritic limestone and a calcite) has been reduced in particulate form, ground, sieved and divided into nine different grain sizes in the range d<0.02÷0.8 mm. Spectroscopic measurements have been performed on all samples using two distinct experimental setup: (a) the Ma_Miss breadboard, and (b) the Spectro-Goniometer setup, both in use in the laboratory at INAF - IAPS. In a previous paper spectral parameters such as the continuum slope and the reflectance level of the spectra have been discussed (De Angelis et al., 2014). In this work we focus our discussion on absorption band parameters (position, depth, area, band slope and asymmetry). We analyzed/investigated the absorption features at 1 μm for the volcanic samples and at 1.4, 1.9 and 2.2 μm for the two carbonate samples. Band parameters have been retrieved from spectra measured with both experimental setup and then compared. The comparison shows that band parameters are mutually consistent: band centers (for carbonate samples) are similar within few percent, and band depth and area values (for carbonates) show consistent trends vs. grain size (decreasing towards coarser grains) for most of samples

Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle.

The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres' orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres' surface indicates that this body is chemically and physically active at the present time

Ambient and cold-temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies

Mg‐phyllosilicate‐bearing, dark surface materials on the dwarf planet Ceres have NH_4‐bearing materials, indicated by a distinctive 3.06 μm absorption feature. To constrain the identity of the Ceres NH_4‐carrier phase(s), we ammoniated ground particulates of candidate materials to compare their spectral properties to infrared data acquired by Dawn's Visible and Infrared (VIR) imaging spectrometer. We treated Mg‐, Fe‐, and Al‐smectite clay minerals; Mg‐serpentines; Mg‐chlorite; and a suite of carbonaceous meteorites with NH_4‐acetate to exchange ammonium. Serpentines and chlorites showed no evidence for ammoniation, as expected due to their lack of exchangeable interlayer sites. Most smectites showed evidence for ammoniation by incorporation of NH_4^+ into their interlayers, resulting in the appearance of absorptions from 3.02 to 3.08 μm. Meteorite samples tested had weak absorptions between 3.0 and 3.1 μm but showed little clear evidence for enhancement upon ammoniation, likely due to the high proportion of serpentine and other minerals relative to expandable smectite phases or to NH_4^+ complexing with organics or other constituents. The wavelength position of the smectite NH4 absorption showed no variation between IR spectra acquired under dry‐air purge at 25 °C and under vacuum at 25 °C to −180 °C. Collectively, data from the smectite samples show that the precise center wavelength of the characteristic ~3.05 μm v_3 absorption in NH_4 is variable and is likely related to the degree of hydrogen bonding of NH_4‐H_2O complexes. Comparison with Dawn VIR spectra indicates that the hypothesis of Mg‐saponite as the ammonium carrier phase is the simplest explanation for observed data, and that Ceres dark materials may be like Cold Bokkeveld or Tagish Lake but with proportionally more Mg‐smectite

Reflectance properties and hydrated material distribution on Vesta: Global investigation of variations and their relationship using improved calibration of Dawn VIR mapping spectrometer

Vesta’s surface albedo variations and hydrated material content share similar spatial distribution. This observation is consistent with carbonaceous chondrite meteorites as a likely source material for dark sur- face units observed by the Dawn spacecraft, as presented by numerous publications. While these deposits have been studied extensively by analysis of data from the Framing Camera (FC) and the Visible and Infrared Spectrometer (VIR), we performed a new analysis based on an improved calibration of VIR. First we identified instrument and calibration artifacts, and we therefore developed corrections of the VIR flat field and response function. Then we developed a photometric correction for Vesta based on the lunar model by Shkuratov et al. (Shkuratov, Yu.G. et al. [1999]. Icarus 141, 132–155. http://dx.doi. org/10.1006/icar.1999.6154), and a semi-analytical inversion of the photometric parameters. This photo- metric model combines minimization of the scattering effects due to the topography (a disk function) and variations of multiple-scattering with phase angle (the phase function) caused by microscopic physical properties of the regolith. The improved calibration and photometric correction enable more accurate analysis of the spectral properties of Vesta’s surface material, especially the reflectance at 1.4 lm and the 2.8 lm hydroxyl absorption band depth. We produced global and quadrangle maps that are used as a common dataset for this Icarus special issue on Vesta’s surface composition. The joint interpretation of both the 1.4 lm reflectance and the 2.8 lm absorption band depth reveals unusual spectral properties for a number of impact craters and ejecta compared to the rest of Vesta. An area including the Bellicia, Arruntia and Pomponia craters, where olivine might be present, has relatively high reflectance and a strong hydroxyl absorption band. Another area in the vicinity of Capparonia crater has a high content of hydrated materials, although with moderate reflectance and typical pyroxene-rich composition. Ejecta blankets west of Oppia crater have a spectral behavior similar to Capparonia, except for the wider and more complex shape of the hydroxyl absorption band. On the other hand, some low-hydrated areas associated to crater floors and ejecta have higher reflectance and steeper spectral slope than most low- hydrated terrains Vesta. A broad lane that extends from Rheasilvia rim at Matronalia Rupes to the north- ern regions hosts little to no hydrated materials and exhibits a moderate spectral slope, similar to Rheasilvia’s basin floor. These properties reinforce the hypothesis that the lane is composed of ejecta from Rheasilvia, as indicated by the distribution of pyroxene compositions by previous results from Dawn. A few small and fresh craters exhibit an association between low-reflectance, little to no hydrated materials and a strong positive spectral slope, suggesting optical effects by opaque coatings, as opposed to carbonaceous chondrite deposits, and possible coarser grains

The spectral imaging facility: Setup characterization

The SPectral IMager (SPIM) facility is a laboratory visible infrared spectrometer developed to support space borne observations of rocky bodies of the solar system. Currently, this laboratory setup is used to support the DAWN mission, which is in its journey towards the asteroid 1-Ceres, and to support the 2018 Exo-Mars mission in the spectral investigation of the Martian subsurface. The main part of this setup is an imaging spectrometer that is a spare of the DAWN visible infrared spectrometer. The spectrometer has been assembled and calibrated at Selex ES and then installed in the facility developed at the INAF-IAPS laboratory in Rome. The goal of SPIM is to collect data to build spectral libraries for the interpretation of the space borne and in situ hyperspectral measurements of planetary materials. Given its very high spatial resolution combined with the imaging capability, this instrument can also help in the detailed study of minerals and rocks. In this paper, the instrument setup is first described, and then a series of test measurements, aimed to the characterization of the main subsystems, are reported. In particular, laboratory tests have been performed concerning (i) the radiation sources, (ii) the reference targets, and (iii) linearity of detector response; the instrumental imaging artifacts have also been investigated. <P /

Nature, formation, and distribution of carbonates on Ceres

Different carbonates have been detected on Ceres, and their abundance and spatial distribution have been mapped using a visible and infrared mapping spectrometer (VIR), the Dawn imaging spectrometer. Carbonates are abundant and ubiquitous across the surface, but variations in the strength and position of infrared spectral absorptions indicate variations in the composition and amount of these minerals. Mg-Ca carbonates are detected all over the surface, but localized areas show Na carbonates, such as natrite (Na_2CO_3) and hydrated Na carbonates (for example, Na_2CO_3·H_2O). Their geological settings and accessory NH_4-bearing phases suggest the upwelling, excavation, and exposure of salts formed from Na-CO_3-NH_4-Cl brine solutions at multiple locations across the planet. The presence of the hydrated carbonates indicates that their formation/exposure on Ceres’ surface is geologically recent and dehydration to the anhydrous form (Na_2CO_3) is ongoing, implying a still-evolving body