Tag: ta2.5

20-EPN2-100: Spectroscopic Identification of Experimental Basalt Alteration Products Under Venus Conditions

Visit by Molly McCanta, University of Tennessee (USA), to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 14 – 20 October 2022

Report Summary: Experiments and thermodynamic modelling clearly show that sulfates are a common alteration product under the high temperature, CO₂-SO₂-rich conditions at the surface of Venus. The exact sulfates present depend on the original basalt composition, with anhydrite (CaSO₄) and thernardite (Na₂SO₄) having been observed in the lab (Reid et al., 2023).

Alteration rates calculated from these experiments suggest that sulfate coatings may develop geologically fast and therefore alteration coatings may obscure the original protolith. Additionally, the spectral features of these high temperature sulfates are not well constrained. Although many critical sulfate minerals are stable to temperatures > 500C, previous analytical data has generally explored sulfate-temperature spectral relations to ~100C. The surface of Venus is significantly hotter at 470C. Thus is makes sense to investigate both the effects of variable thickness sulfate coatings and the spectral properties of sulfates under Venus surface conditions to gain a better understanding of their behaviour.

The next set of Venus missions will have observational capabilities in the thermal emission spectrum (range) and high T sulfate spectra are presented in another paper (Dyar ref); here we present data for the effects of high T on visible near-infrared (VNIR) sulfate spectra. In addition, we have conducted experiments to determine the effects of sulfate coating thickness on the underlying surface spectra. The data presented may help determine future mission capabilities to both recognise and analyse sulfate-bearing materials under high T conditions as well as constrain the original, unaltered surface composition.

20-EPN2-097: Venus-Temperature Emissivity Experiments on Pure Minerals

Visit by Melinda Darby Dyar, Mount Holyoke College (USA), to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 14 – 20 October 2022

Report Summary:

This project supports a collaboration between the US and personnel at the Planetary Spectroscopy lab in DLR Berlin to understand the interrelationships among high temperature emissivity and high or ambient temperature reflectance measurements of rocks and minerals present on the surfaces of rocky bodies (planets, moons, and asteroids). We are investigating the extent to which spectral features in the near-IR wavelength region shift and change in intensity as a function of temperature and measurements type. These changes are easiest to understand when comparisons can be made for single mineral species.

With Europlanet support, we acquired hemispherical and bidirectional reflectance and emissivity spectra of planetary-analog minerals at the PSL at DLR Berlin. Minerals studied included pyroxene, feldspar, olivine, sulfates, and calcite minerals. Significant differences between hemispherical and biconical reflectance data were observed; as we write up the results, we will explore the underlying physical characteristics of each mineral group and relate them to the magnitude of those changes. We also observed significant differences between bidirectional reflectance spectra and emissivity results in preliminary results. This outcome suggests that laboratories seeking to make Venus-relevant measurements cannot draw conclusions about spectral intensities on the basis of bidirectional data.

20-EPN2-048: Heating effects on the spectral reflectance properties of carbonaceous chondrite meteorites

Visit by Edward Cloutis, University of Winnipeg (Canada), to TA2 Facility 5 – DLR Planetary Spectroscopy Laboratory (Germany).
Dates of visit: 28 August – 2 September 2022

Report Summary: Carbonaceous chondrites are likely derived from dark (C-class) asteroids. Sample return missions to dark asteroids (JAXA Hayabusa-2, OSIRIS-REx) will allow us to link specific meteorites to these possible parent bodies. The compositions of the sample return target asteroids (Ryugu and Bennu) are currently unknown, as are the compositions of other dark asteroids. Dark asteroids are important scientific targets because they may have delivered prebiotic organic molecules to the early Earth.To help address how we can determine the compositions of dark asteroids, particularly whether they are primitive, aqueously-altered, and/or heated, we conducted a series of experiments at PSL designed to address this.

Specifically, we performed heating experiments, in vacuum, on clay minerals present in carbonaceous chondrite meteorites, and measured their subsequent spectral reflectance properties, as well as on samples heated in previous experiments (clays, carbonaceous chondrites, carbonaceous chondrite analogues), focusing on the most diagnostic spectral feature relevant to dark asteroids – the 3 micron region hydroxyl/water absorption band. The results are still being analysed, but it appears that heating in vacuum and exposure to vacuum cause changes in the depth and shape of this absorption feature, as well as the albedo, spectral slope, and appearance of additional absorption features. The results of this study will provide important constraints into the composition and history of dark asteroids.