Our main objective is to study Canadian Arctic gossans as an analogue to ancient hydrothermal systems on the planet Mars. The gossans are characterized by ochre-coloured surface deposits that are quite easily recognized using satellite images (figure 1). However, the composition of these gossans can vary at local scale (one meter or less), which requires remote sensing instruments closer to the outcrop to determine its mineralogical composition. The precise elemental composition and the potential for preservation of the biosignature must be obtained through the analysis of the samples: this is an information that cannot be obtained remotely.
We therefore propose to study the composition of the gossans at the spatial scales of the orbit, the rover and the sample (figure 2). From this, the specific objectives presented under figure 2 are defined, which have been chosen with the aim of realizing a methodology similar to the one used during the Martian missions.
Gossans have been detected at various locations in the Canadian Arctic and some have already been studied in the field. Our study area is located near the McGill Arctic Research Station (MARS - not to be confused with the title of our research project T-MARS, Terrestrial Mineral Analysis by Remote Sensing), on Axel Heiberg Island in Nunavut. This region was found to be particularly rich in gossans and evaporite domes, which is consistent with the presence of a paleo-hydrothermal system [1,2,3].
The first step of our project is to establish the regional context and remote predictive mapping  of the gossans on Axel Heiberg Island, at a spatial scale of about ten to a hundred meters. These maps will be useful in preparation for the field campains and the work that will be carried out on site . The geoscientific data used for the mapping include:
- geological maps provided by the Geological Survey of Canada;
- topographic maps;
- satellite images from sensors such as Landsat, Spot, Ikonos and WorldView;
- the Arctic Digital Elevation Model (ArcticDEM).
In our case, we will produce a predictive map of the gossans on Axel Heiberg Island to determine their number, which ones are accessible for field sampling and which seem to be the most interesting scientifically, based on their regional context and composition. The process of remote predictive mapping is analogous to the use of data acquired by remote sensing instruments in orbit around the planet Mars, in order to determine the most promising landing site for a lander or a rover .
The second step of our project is to investigate the composition of gossans horizontally, at a spatial scale of meter to centimeter. The research will be conducted on Axel Heiberg Island during two filed campaigns in the summers of 2021 and 2022 in order to visit as many outcrops as possible and to complete the data sampling. This step is analogous to the scientific operations that would be carried out by a rover or a drone on Mars.
Acquire remote sensing data from a drone
- Measured parameter: reflectance of gossans
- Measuring instrument: hyperspectral imager mounted on board a drone
- Spatial scale of measurement: tens of centimeters
- Utility: to establish the surface mineralogical composition at different locations on the gossans and to validate the remote sensing observations acquired in orbit by the satellites
Acquire localized remote sensing data
- Measured parameter: localized reflectance of gossans
- Measuring instrument: portable spectroradiometer
- Spatial scale of measurement: centimetric
- Utility: to establish the mineralogical composition at the surface at different locations on the gossans and to validate remote sensing observations acquired at coarser resolutions
Determine the elemental composition of materials
- Measured parameter: elemental composition of the different materials present in the outcrops.
- Measuring instrument: Laser Induced Breakdown Spectroscopy (LIBS technology)
- Spatial scale of measurement: millimetric
- Utility: to assess the variability in the composition of the gossans and to select samples for more detailed laboratory analysis
Our approach mimics rover operations on Mars. In fact, LIBS technology is used by the ChemCam instrument on the Mars Curiosity rover , and is also used by the SuperCam instrument on the Mars 2020 rover.
The third step of our project is to investigate the composition of the gossans vertically, at a spatial scale of meter to centimeter. The research that will be conducted on the field at Axel Heiberg Island is analogous to the scientific operations that could be conducted by a Martian rover using a core drill and remote sensing instruments. Past exploration of the Canadian Arctic gossans on Victoria Island and Axel Heiberg Island has revealed that the gossans are stratified, but that the stratification of the different gossans varies [1,7]. A closer investigation of the stratigraphy will increase the knowledge of the vertical composition of gossans and their formation and evolution processes. It will also allow us to target the specific layers that most probably host life (and potentially have hosted life on Mars in the past).
Collecting cores in gossans
We will first collect mini cores in paleo-hydrothermal systems and in the alteration halos around the gossans (i.e. the contact zone between the gossans and the bedrock). These cores will be studied in the laboratory using ELEMISSION's Coriosity LIBS instrument.
Acquire multispectral images of a cross-sectional view of gossans
We will then dig trenches at least one meter deep into the selected gossans to obtain a cross-sectional view. This process is analogous to a rover acquiring a coring sample (for example, the corer of the next ExoMars 2020 mission of the European Space Agency is expected to reach depths of at most two meters). High-resolution multispectral images of these sections will be acquired to determine the stratigraphy of the outcrop. This multispectral information will allow to distinguish and categorize the different layers. The sensor that will be used is similar to the Panoramic Camera (Pancam) which was on board the Spirit and Opportunity rovers for Mars exploration, or to the Mastcam-Z instrument which is on board the Mars 2020 rover [8,9]. These types of cameras allow to derive a first-order spectral analysis of the minerals present.
Establish the mineralogical composition of the layers
We will finally acquire samples and hyperspectral observations for each identified layer. This will be done using a portable spectroradiometer and its contact probe to establish the precise mineralogical composition of each layer. Samples will be collected and returned to the laboratory for further analysis. Portable LIBS and Raman spectroscopy instruments will be used to understand the vertical composition of the gossans. LIBS technology can detect, identify and quantify the chemical composition of any material, while Raman spectroscopy provides detailed information on chemical structure, phase, polymorphy, crystallinity and molecular interactions.
The fourth step of our project is to investigate the spectral signature, the composition and the biosignature content of the reported samples. The analyses will be conducted in different laboratories by the students, under the supervision of the researchers. Bringing back to the laboratories samples similar to those collected on Mars for further study is in line with the objectives of the Mars 2020 rover, for which the samples will be acquired, sealed, stored on board and then deposited on the surface of Mars to be retrieved by a later mission.
Investigate the spectral signature of samples
We will characterize the spectral reflectance of each sample in the spectroscopy laboratory of Dr. Lemelin at the Université de Sherbrooke. The reflectance spectra will be acquired using a portable spectroradiometer and following the specifications of the Canadian Space Agency's (CSA) planetary analogue material suite , which details standardized parameters for measurements. The most relevant spectra will then be shared with the CSA's planetary analogue materials suite under the Mars analogue section .
Investigate the composition of samples
We will characterize the composition of the samples using X-ray fluorescence (XRF) and X-ray diffraction (XRD) instruments at the Facility for Electron Microscopy Research at McGill University, under the supervision of astrobiologist Dr. Léveillé. FRX instruments provide information on the elemental and chemical composition of the samples, while the DRX provides information on the mineralogy of the material.
The mini cores samples will be studied differently from the soil samples. We will use the Coriosity LIBS instrument from ELEMISSION to analyze the elemental and mineralogical composition of the core samples. This innovative instrument is the only LIBS instrument that allows automated multi-element analysis and a mineralogical analysis at high speed (1000 measurements per second) and high spatial resolution (50 μm) .
Investigate the biosignature of samples
The biosignature content of the samples will be analyzed at McGill University under the supervision of astrobiologist Dr. Léveillé. More specifically, we will target the elemental and textural signatures of jarosite and associated minerals. While the preservation of organic matter is expected to be low on Mars, minerals may retain information for much longer periods of time as they are not subjected as much to oxidative processes and radiation effects as organic matter [12,13]. For these reasons, minerals related to hydrothermal systems and alteration minerals are considered as primary exploration targets on Mars [14,15].
Jarosite and related iron sulphate minerals are generally produced from low-temperature aqueous alteration in sulfide-rich hydrothermal systems [16,17]. Thus, they are of particular interest on Mars and in our study region. It has recently been shown that jarosite formed without the presence of life has spectral differences from jarosite formed in the presence of life . It has also been shown that the study of terrestrial occurrences of jarosite can help to reinterpret the history of the presence of water on Mars, on the basis of data collected by rovers. The conclusion is that the presence of jarosite, rather than suggesting acidic and water-limited environments, suggests much more habitable conditions at the beginning of Mars .
Hydrothermal systems on Earth are well known to contain diverse microbial communities, many of which leave characteristic biosignatures in rocks and minerals, including mineralized filamentous forms [16,17]. The advantage of investigating samples in the laboratory is that a high level of detail can be obtained regarding the interactions between microbes, organic matter and mineral matter. In fact, the study of samples collected from Mars may be the only way to conclusively detect the past presence of life.
Our approach can be used to investigate biosignatures and develop an unambiguous set of them. In addition to simulating the analysis of samples from the planet Mars, this effort will also help to better understand the preservation of biosignature in Mars-like minerals over geological time, in cold and arid climates. We will combine LIBS and Raman spectroscopy in the laboratory to characterize samples and identify biosignatures. These will be further investigated using a scanning and transmission electron microscope at the Facility for Electron Microscopy Research at McGill University.
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