Authored by Dr. Jessica Flahaut (Laboratoire de Géologie de Lyon, France), Dr. Janice Bishop (SETI Institute, California), Mélissa Martinot (VU University Amsterdam, the Netherlands), Nicci Potts (the Open University, United Kingdom and 2015 Goetz Program awardee), Dr. Simone Silvestro (Istituto Nazionale di Astrofisica, Italy) and collaborators G.R. Davies, D. Tedesco, I. Daniel and C. Quantin (see references). 

Dr. Jessica Flahaut is a planetary geologist at CNRS/CPRG Nancy, France. Her fields of expertise include remote sensing and spectroscopic studies of Mars and the Moon, landing site selection and characterization for future missions and terrestrial geology / analog field studies.

This project was funded by an NWO (Netherlands Science Organization) VENI fellowship attributed to Dr. Jessica Flahaut. Dr. Janice Bishop is grateful for support from the NASA Astrobiology Institute.

The identification and characterization of hydrated minerals, within ancient aqueous environments on Mars, are a high priority for determining the past habitability of the red planet. Few studies, however, have focused on characterizing entire mineral assemblages as this is often difficult to determine from remote sensing data, even though this could aide our understanding of past environments. This is especially true for the sulfate-rich deposits, which are thought to mark a transition to more acidic conditions at the Martian surface about 3.5 Ga. This transition would coincide with a period of global climate change. As a result, quantitative constraints on Martian habitability during the ‘Mars global change’ era remain poor.

In this project, we used both spaceborne and field analyses to investigate the mineralogy of two terrestrial Mars analog sites. We compared these terrestrial analog data to Mars sulfate-rich deposits which provided new, critical, information on geologic environments and habitability conditions on Mars at a time of planetary-scale climate change.

For more info on sulfate-rich deposits on Mars, see (non-exhaustive list):

  • Gendrin, Aline, et al. “Sulfates in Martian Layered Terrains: the OMEGA/Mars Express View.” Science, 11 Mar. 2005, pp. 1587–1591. DOI: 10.1126/science.1109087
  • Bibring, Jean-Pierre, et al. “Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data.” Science, 21 Apr. 2006, pp. 400–404. DOI: 10.1126/science.1122659
  • Murchie, S. L., et al. (2009), A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter, J. Geophys. Res., 114, E00D06, DOI:10.1029/2009JE003342.
  • Bethany L. Ehlmann and Christopher S. Edwards. Annual Review of Earth and Planetary Sciences 2014 42:1291-315 
  • Flahaut, J., Massé, M., Le Deit, L., Thollot, P., Bibring, J.P., Poulet, F., Quantin, C., Mangold, N., Michalski, J. and Bishop, J.L., (2014). Sulfate-Rich Deposits on Mars: A Review of Their Occurrences and Geochemical Implications. LPI Contributions, 1791, p.1196.

Two Mars analog sites were selected:

1. The Atacama desert salt flats (northern Chile, visited March 2015): They represent more than 100,000 km2 of chloride and sulfate salt deposits. These salts precipitated from the evaporation of groundwater in enclosed depressions, along and within, the Andes volcanic range. We visited five salt flats (also named salars) of various geological settings and brine compositions to survey their mineralogic diversity and collected about 60 samples for complementary geologic (Raman, XRD, etc) and astrobiologic (amino acids, DNA extraction) analyses. During this campaign we were very fortunate to receive the support of the Goetz Instrument Program of ASD Inc (2015, attributed to Nicola Potts) and the European Southern Observatory (ESO), which hosted us at its local instrument camp, the Atacama Pathfinder Experiment (APEX) Sequitor base.

2. The Solfatara volcanic crater (Italy, visited in September 2015): This 4000-year-old crater is located at the center of the Phlegrean Fields caldera, just north of Naples. Volcanic activity in the Phlegrean Fields includes thermal pools, fumarole emissions, and seismic activity. Fumarole emissions are most active within the Solfatara crater (CO2, H2O, H2S, and CH4, up to 200°C), and lead to weathering of the local ignimbrite rocks into various types of sulfates. This campaign was supported by the ENS Lyon Raman team, which lent us a portable Raman spectrometer for complementary analyses and the Solfatara managing team, who welcomed us at the campsite within the crater.

In the Atacama desert, field sites were selected based on mineralogic diversity, as suggested by spaceborne imagery, combined with accessibility i.e., available roads or tracks, protected natural areas, and potential landmines. Several E-W and N-S transects were sampled in the main salar; the salar de Atacama, which lies at relatively low elevation (2500 m), on a sedimentary basement. Four salars were visited at higher elevations (>4000 m) within the Andes. At the Solfatara crater, seven sites were sampled and classified into 3 categories based on their different vent temperatures, which also related to distinct mineralogic assemblages.

The location and morphology of the outcrops was documented with a field tablet equipped with a Geographic Information System (GIS) application. In situ mineralogy was determined from VNIR reflectance spectra measured with an ASD Fieldspec 4 Hi-Res instrument. The ASD Fieldspec 4 Hi-Res spectrometer collects visible and near-infrared (VNIR) spectra in the 350 – 2500 nm spectral domain with three detectors (VNIR: 300-1000, SWIR-1: 1001-1800, SWIR-2: 1801-2500 nm) with a spectral resolution of 3 nm in the 350-1000 nm range, and 8 nm in the 1001-2500 nm range. In the Atacama desert, all spectra were acquired in the field at a distance of ~ 10 cm from the outcrops, using the bare fiber inserted directly in the pistol grip. As the atmospheric water vapor content is very low (< a few %) in the Atacama there was no need for a contact probe. At la Solfatara, spectra were acquired with various setups including the contact probe, the bare fiber inserted in the pistol grip, and the 8 degree fore optic accessory. Spectra were compared with spectra of reference minerals from the USGS and CRISM spectral libraries for mineral identification (e;g., Clark et al., 2006; Murchie et al., 2007).

We identified various types of Ca-, Na-sulfates, chlorides, borates, clays and carbonates in the Atacama salt flats based on VNIR spectra. Our study allowed us not only to demonstrate mineralogical zonation within the salars, but also to explore the mineralogical diversity observed between the different salars (and correlate it with bedrock composition and brine chemistry; see Flahaut et al., AGU2015, in reviews).

At the Solfatara site, we identified various hydrated Al, Fe and Ca-sulfates, clays and opaline silica. Native sulfur and arsenic sulfides can also be recognized thanks to their diagnostic colors and shapes. We found that various mineralogic assemblages characterize the vents of different temperatures (see Flahaut et al., LPSC2016). In contrast to the Atacama rocks, most of the material at la Solfatara is amorphous, leading to inconclusive Raman and XRD analyses. This kind of multiple instrument field work provides data necessary for interpreting the results from current and future Mars missions, where it is sometimes difficult to correlate the results from different instruments.

An important outcome of this work is that not all of the minerals we observed/sampled in the field were referenced in existing libraries, thus highlighting the need to keep extending reference libraries of terrestrial salts. Additionally, not all of the minerals exhibit spectral features in the VNIR, but these could be identified with alternative methods in the field and/or in the lab. We found that thin, salt crusts or coatings or even low abundance mixture were efficient at masking local bedrock signatures as sulfate salts are spectrally dominant over most minerals. These observations allowed us to explore the limitations of relying on VNIR remote sensing observations on Mars solely for mineral identification and identify future stages into the characterization of the entire mineralogic assemblage / the petrology of the surface rocks. Our next step is to compare mineral associations and settings with specific sulfate-rich deposits on Mars in order to better constrain sedimentary and alteration processes on Mars and reconstruct paleo- surface conditions there.

For more info, please refer to:

  • Flahaut J., M. Martinot, J. L. Bishop, G.R. Davies and N. Potts (2017), Remote sensing and in situ mineralogic survey of the Chilean salars: An analog to Mars evaporate deposits. Icarus, 282, 152–173, DOI:10.1016/j.icarus.2016.09.041.
  • Flahaut J., J. L. Bishop, I. Daniel, S. Silvestro, D. Tedesco and C. Quantin, 2016. Spectral Characterization of the Sulfate Deposits at the Mars Analog Site of La Solfatara (Italy), 47th Lunar and Planetary Science Conference, abstract #2233. (see poster below).
  • Bishop, and Janice. “Combined VNIR and Raman Spectroscopy of the Atacama Salt Flats as a Potential Mars Analog.” Abstract: From Source to Damage: A Case Study of the M7.2 October 2013 Bohol Earthquake (2015 AGU Fall Meeting), Agu, (see poster below).
  • Flahaut J. et al. 2015. Combined VNIR and Raman spectroscopy of Mars analogue sediments from the Atacama salt flats, The Sixth Moscow Solar System Symposium.
  • Flahaut J., M. Martinot, N. J. Potts, and G. R. Davies, 2015. VNIR spectroscopy of the Atacama salars: An analogue study for Mars evaporate deposits, European Planetary Science Congress, abstract # EPSC2015-84.