In-situ measurement and sampling of Martian analogues in the Rio Tinto area in support of the Ma_MISS scientific activity

Introduction

The selected landing site of the ExoMars mission (Oxia Planum) [1] shows mineralogical and morphological evidence that it was characterized by a hydrothermal history and by a long duration of aqueous superficial activity [2; 3]. These factors are consistent with conditions favourable to life development. In this framework, we planned a field campaign in the Rio Tinto [4] area (Europlanet TA1 facility 2) where to perform a set of VIS-NIR measurements using our portable spectrometer. In addition, for each analyzed mineral/rock on-field, we collect a representative sample to be measured with the Ma_MISS instrument laboratory model. 

Fig.1: TA1.2 Rio Tinto, south-west Spain a very acidic 100 km river with intense red dark colour (credits F. Gomez).

The Ma_MISS instrument

Ma_MISS is the Visible and Near-Infrared miniaturized spectrometer hosted in the drill system of the ExoMars rover that will characterize the mineralogy and stratigraphy of the excavated borehole wall at different depths (<2 m) [5]. Ma_MISS with a spectral range of 0.5–2.3 μm, a spectral resolution of about 20 nm in the IR, a SNR~100, and a spatial resolution of 120 μm will accomplish the following scientific objectives: (1) determine the composition of the subsurface materials; (2) map the distribution of the subsurface H₂O and hydrated phases; (3) characterize important optical and physical properties of the materials (e.g., grain size); (4) produce a stratigraphic column that will provide information on the subsurface geology. Ma_MISS will operate periodically during pauses in drilling activity and will produce hyperspectral images of the drill’s borehole.

Field activity

During the field campaign, we perform a set of VIS-NIR (0.35 – 2.5 μm) measurements using our ASD FieldSpec4 portable spectrometer on biosignatures-bearing rocks and acidic alteration products. For each selected lithotype we collect several reflectance spectra using solar light as the light source and a 99% Spectralon target as a reference in the VIS-NIR range, with particular attention to those that hypothetically host organic matter in the form of bacterial communities. In addition, for each measured mineral/rock we collect a representative sample to be used for the laboratory measurements with the Ma_MISS laboratory model. With this setup, it is possible to perform measurements with samples in different configurations (powders, slabs, or holed rock blocks); hence, we collect samples with different specific dimensions. In the case of incoherent sediments/salts, we sample a minimum amount of 20-30 g. On the contrary, in the case of coherent samples, we collect blocks with a maximum size of 10x10x10 cm, which are the optimal dimensions useful for performing the drilling operations and in-hole measurements with the DAVIS setup [6,7]. For each collected sample, we record the following data at the time of collection: imagery of the context and the sampling site with a reference scale, the three-dimensional orientation of the sample, and the geographic coordinates at the collection point using a GNSS dual-frequency GPS. Every sample is sealed in a specific container to avoid any contamination [8]. The samples’ metadata are registered in the System for Earth Samples Registration (SESAR) for long-term archival of the physical samples which can be retrieved from a unique ISGN code (isgn.org) for referencing in this and future projects.

Laboratory activity

The collected samples were measured with the DAVIS (Drill for Analogues and Visible-Infrared Spectrometer) setup at the INAF-IAPS laboratories. This laboratory facility is constituted by a drilling tool that reproduces the ExoMars Drill functionality (Laboratory Drill, LD [6]) and by a measurement tool, reproducing Ma_MISS optical characteristics (Ma_MISS Optical Tool, MOT [7]). Consisting of spare elements of the flight instrument, the DAVIS setup can be considered an instrument completely comparable to the one that will investigate the Martian subsurface. For this reason, the measurements on the collected samples become very important for instrument characterization and future data interpretation. The collected sample blocks are drilled to obtain a hole with the same characteristics as those that the ExoMars drill will do on Mars. Finally, we perform a series of in-hole spectral scans to characterize the chemical-physical properties of the collected samples. The data collected on-field and in the laboratory are analyzed and compared to reconstruct the composition of the analyzed samples. We will focus our efforts on any spectral signature related to the presence of biomarkers in the collected data since we know that the Ma_MISS tool can aid in detecting organics [9] in the Martian subsoil, which is one of the main scientific objectives of the ExoMars mission.

Conclusions

In this work, we describe the procedures followed during our geological field analysis campaign in the Rio Tinto area. This geologically/biologically well-documented site with its rock/water/biology interaction represents an ideal open-air laboratory where to collect spectral data and samples useful for testing the ExoMars/Ma_MISS spectrometer. The scientific results obtained by this and previous works made with other drilling equipment [10] and with other scientific instruments [11] confirm that this type of activity in the Rio Tinto area site is important for enriching the scientific community's grasp on the Martian environment and for obtaining key information on the mineralogical and geochemical evolution of the Martian surface/subsurface. In addition, this work provides crucial preparation for the exploitation and interpretation of the scientific data that the Ma_MISS instrument will supply during the active phase of the mission. This activity is also useful for defining the priorities of the astrobiological objectives on the ground.

Acknowledgements

This work is supported by the Italian Space Agency grant ASI-INAF n. 2017-412-H.0. Ma_MISS is funded by ASI and INAF. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

References

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