ExoMars Rover Research Articles

Defining Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary Missions Using a Statistical Method.

Biomarker molecules, such as amino acids, are key to discovering whether life exists elsewhere in the Solar System. Raman spectroscopy, a technique capable of detecting biomarkers, will be on board future planetary missions including the ExoMars rover. Generally, the position of the strongest band in the spectra of amino acids is reported as the identifying band. However, for an unknown sample, it is desirable to define multiple characteristic bands for molecules to avoid any ambiguous identification. To date, there has been no definition of multiple characteristic bands for amino acids of interest to astrobiology. This study examined l-alanine, l-aspartic acid, l-cysteine, l-glutamine and glycine and defined several Raman bands per molecule for reference as characteristic identifiers. Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA. The number of characteristic bands defined were 10, 12, 12, 14 and 19 for l-alanine (strongest intensity band: 832 cm-1), l-aspartic acid (938 cm-1), l-cysteine (679 cm-1), l-glutamine (1090 cm−1) and glycine (875 cm-1), respectively. The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation. It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

Iceland doubles for Red Planet in camera test

To a Martian, Iceland's volcanic landscape might look a bit like home. No wonder the camera for the next Mars rover just did a test run there. The PanCam (for Panoramic Camera) is set to travel aboard the European Space Agency's ExoMars rover in 20l9. It looks like a three-eyed monster, says Claire Cousins, a planetary scientist at the University of Edinburgh UK. Two eyes on the right and left of the unit scan the terrain for noteworthy features. They also switch between filters set to different wavelengths in order to pick up subtle spectral properties of minerals--a clue to their composition. Nestling between the two is a high-resolution camera.

Avoiding misidentification of bands in planetary Raman spectra

Raman spectroscopy has been identified as a powerful tool for astrobiology and remote robotic planetary exploration. It can be used to identify and characterise rock matrices, mineral inclusions and organic molecules and is demonstrably effective at identifying biomarkers, or indicators of biological activity. The ExoMars rover, jointly operated by the European and Russian Federal Space Agencies, will carry the first Raman spectrometer into space when it launches in 2018 and two further Raman instruments have recently been announced as part of the payload onboard the National Aeronautics and Space Administration's Mars 2020 rover. Each of these spectrometers however will, by necessity, have poorer resolution than the most sophisticated laboratory instruments because of mass, volume and power constraints and the space readiness of the requisite technologies. As a result, it is important to understand the minimum instrument specification required to achieve the scientific objectives of a mission, in terms of parameters such as spectral resolution and laser footprint size. This requires knowledge of the target minerals and molecules between which there may be ambiguity when identifying bands in spectra from geological samples. Here, we present spectra from a number of Mars analogue samples that include a range of such molecules, highlighting where such confusion may occur and identifying the most useful bands for differentiation. It is recommended that a Raman spectrometer achieves a resolution of at least 3 cm−1 and covers a spectral range from 100 to 4000 cm−1 in order to differentiate between all of the target molecules presented here. Copyright © 2015 John Wiley & Sons, Ltd.

Testing the ability of the ExoMars 2018 payload to document geological context and potential habitability on Mars

The future ExoMars rover mission (ESA/Roscosmos), to be launched in 2018, will investigate the habitability of the Martian surface and near subsurface, and search for traces of past life in the form of textural biosignatures and organic molecules. In support of this mission, a selection of relevant Mars analogue materials has been characterised and stored in the International Space Analogue Rockstore (ISAR), hosted in Orléans, France. Two ISAR samples were analysed by prototypes of the ExoMars rover instruments used for petrographic study. The objective was to determine whether a full interpretation of the rocks could be achieved on the basis of the data obtained by the ExoMars visible-IR imager and spectrometer (MicrOmega), the close-up imager (CLUPI), the drill infrared spectrometer (Ma_Miss) and the Raman spectrometer (RLS), first separately then in their entirety. In order to not influence the initial instrumental interpretation, the samples were sent to the different teams without any additional information. This first step was called the “Blind Test” phase. The data obtained by the instruments were then complemented with photography of the relevant outcrops (as would be available during the ExoMars mission) before being presented to two geologists tasked with the interpretation. The context data and photography of the outcrops and of the samples were sufficient for the geologists to identify the rocks. This initial identification was crucial for the subsequent, iterative interpretation of the spectroscopic data. The data from the different spectrometers was, thus, cross-calibrated against the photographic interpretations and against each other. In this way, important mineralogical details, such as evidence of aqueous alteration of the rocks, provided relevant information concerning potential habitable conditions. The final conclusion from this test is that, when processed together, the ExoMars payload instruments produce complementary data allowing reliable interpretation of the geological context and potential for habitable environments. This background information is fundamental for the analysis and interpretation of organics in the processed Martian rocks.

Dynamic Bayesian Networks for Fault Detection, Identification, and Recovery in Autonomous Spacecraft

This paper describes how to exploit the modeling features and inference capabilities of dynamic Bayesian networks (DBN), in designing and implementing an innovative approach to fault detection, identification, and recovery (FDIR) for autonomous spacecrafts (e.g., a Mars rover). In particular, issues like partial observability, uncertain system evolution and system-environment interaction, as well as the prediction and mitigation of imminent failures can be naturally addressed by the proposed approach. The DBN framework can augment the modeling and analytical power of standard FDIR methodologies, while still being able to be integrated into the usual system modeling procedures (like, for instance, fault tree analysis). An FDIR cycle composed of the tasks of diagnosis (identification of the current state of the system), prognosis (identification of the future state under the current conditions), and recovery (selection of the best set of actions the autonomous system can perform, in order to avoid critical situations) is introduced and characterized through a DBN model. In particular, by considering the execution of recovery actions in response to either a current or a future abnormal situation, both reactive as well as preventive recovery can be addressed respectively. The proposed approach has been implemented in an on-board software architecture called Anomaly resolution and prognostic health management for autonomy (ARPHA), realized during the Verifim study funded by the European Space Agency and jointly performed with Thales/Alenia Italy. We report on some of the results obtained by performing a case study concerning the FDIR analysis of the power supply system of the ExoMars rover, by considering different anomalous and failure simulated scenarios; we conclude that ARPHA is able to properly detect and deal with the simulated problems.

Raman spectroscopy as a screening tool for ancient life detection on Mars.

The search for sp(2)-bonded carbonaceous material is one of the major life detection strategies of the astrobiological exploration programmes of National Aeronautics and Space Administration and European Space Agency (ESA). The ESA ExoMars rover scheduled for launch in 2018 will include a Raman spectrometer with the goal of detecting sp(2)-bonded carbonaceous material as potential evidence of ancient life. However, sp(2)-bonded carbonaceous material will yield the same Raman spectra of well-developed G and D bands whether they are synthesized biologically or non-biologically. Therefore, the origin and source of sp(2)-bonded carbonaceous material cannot be elucidated by Raman spectroscopy alone. Here, we report the combined approach of Raman spectroscopy and gas chromatography-mass spectrometry biomarker analysis to Precambrian sedimentary rocks, which taken together, provides a promising new methodology for readily detecting and rapidly screening samples for immature organic material amenable to successful biomarker analysis.

ESA ExoMars: Pre-launch PanCam Geometric Modeling and Accuracy Assessment

Abstract. ExoMars is the flagship mission of the European Space Agency (ESA) Aurora Programme. The mobile scientific platform, or rover, will carry a drill and a suite of instruments dedicated to exobiology and geochemistry research. As the ExoMars rover is designed to travel kilometres over the Martian surface, high-precision rover localization and topographic mapping will be critical for traverse path planning and safe planetary surface operations. For such purposes, the ExoMars rover Panoramic Camera system (PanCam) will acquire images that are processed into an imagery network providing vision information for photogrammetric algorithms to localize the rover and generate 3-D mapping products. Since the design of the ExoMars PanCam will influence localization and mapping accuracy, quantitative error analysis of the PanCam design will improve scientists’ awareness of the achievable level of accuracy, and enable the PanCam design team to optimize its design to achieve the highest possible level of localization and mapping accuracy. Based on photogrammetric principles and uncertainty propagation theory, we have developed a method to theoretically analyze how mapping and localization accuracy would be affected by various factors, such as length of stereo hard-baseline, focal length, and pixel size, etc.

Potential for analysis of carbonaceous matter on Mars using Raman spectroscopy

The ESA/Roscosmos ExoMars rover will be launched in 2018. The primary aim of the mission will be to find evidence of extinct or extant life by extracting samples from the subsurface of Mars. The rover will incorporate a drill that is capable of extracting cores from depths of up to 2m, a Sample Preparation and Distribution System (SPDS) that will crush the core into small grains and a suite of analytical instruments. A key component of the analytical suite will be the Raman Laser Spectrometer (RLS) that will be used to probe the molecular and mineralogical composition of the samples. In this work we consider the capability of the proposed Raman spectrometer to detect reduced carbon (possibly associated with evidence for extinct life) and to identify the level of thermal alteration/maturity. The Raman analysis of 21 natural samples of shale (originating from regions exhibiting different levels of thermal maturity) is described and it is shown that reduced carbon levels as low as 0.08% can be readily detected. It is also demonstrated that the Raman spectra obtained with the instrument can be used to distinguish between samples exhibiting high and low levels of thermal maturity and that reduced carbon can be detected in samples exposed to significant levels of oxidation (as expected on the surface of Mars).

Automated algorithms to identify and locate grains of specific composition for NIR hyperspectral microscopes: Application to the MicrOmega instrument onboard ExoMars

MicrOmega is an NIR hyperspectral microscope that has been selected as part of the ExoMars rover payload. We demonstrate here that this instrument has the capability through automated algorithms to identify and locate grains of interest (composition-wise) within a collected sample that could be further targeted by other instruments within the ExoMars payload. Results will also be used to perform an optimized compression of the data, with regard to the relevance of the different grains, in order to limit the volume of downloaded data. The algorithms that we have developed, using combined spectral criteria and different tests to avoid false positive, have proven to be both highly robust and efficient. They will be used onboard ExoMars rover, and could also be adapted for future robotic missions involving hyperspectral microscopes.

Analysis of the scientific capabilities of the ExoMars Raman Laser Spectrometer instrument

The Raman Laser Spectrometer (RLS) is part of the payload of the 2018 ExoMars rover. The Sample Preparation and Distribution System (SPDS) of the rover will crush samples acquired from down to two meters depth under the Martian surface, and provide them to the RLS instrument in the form of flattened powdered samples. The RLS instrument will acquire a minimum of 20 points on the flattened surface of the samples. To be able to obtain the maximum scientific return from the instrument once on Mars, a simulator of the SPDS system has been built to perform a series of experiments in a representative scenario. The crushing process implies the loss of rock structure and texture and, hence, the geological context of the samples. However, qualitative analysis with the RLS simulator on powdered natural samples and rocks showed that the RLS is capable of detecting carbonaceous material occurring in trace amounts in one of the rock samples (a silicified volcanic sand), more easily than with the same analysis on bulk. Furthermore, it is shown that minor phases in carbonate cements that cannot be detected by Raman in the bulk sample can be detected in the powder, thus allowing the identification of all the carbonate phases present in the cement crust. In order to quantify the detection threshold of the instrument, further analysis on controlled samples were performed. The results with the RLS SPDS simulator showed that the instrument can reach detection thresholds down to 1 % on powdered samples. Furthermore, analysis of controlled mixtures showed that performing a very simple intensity-based statistical analysis of the spectra can provide semi-quantification of the abundance of the mineral species with quite linear calibration curves.

Morpho-stratigraphic characterization of a tufa mound complex in the Spanish Pyrenees using ground penetrating radar and trenching, implications for studies in Mars

The Isona tufa mound complex (ITMC), associated with artesian springs of the Areny-Montsec aquifer, Spanish Pyrenees, is a potential analog for water constructed landforms on Mars. We used Ground Penetrating Radar (GPR), trenching, sedimentological description of exposures, and radiocarbon and U-series dating methods for the geological characterization of the ITMC. Preliminary geomorphological mapping combined with sedimentological analyses permitted the recognition of the different facies and their spatial distribution. GPR surveys conducted next to an outcrop and a trench provided electromagnetic wave velocity in tufas (0.09 and 0.11 m ns−1) and determined the correspondence of the radar signatures with facies types. This was used to reconstruct the tufas internal structure and the depositional stages for two different contexts: (1) an upper unit representing the morpho-stratigraphic record of paleosprings – Tufa 1 – composed of relict tufa mounds older than 350 ka BP; and (2) a lower unit – Tufa 3 – associated with groundwater aquifer outlets (Basturs Lakes). The GPR data allowed depicting the signatures for the vent, pool, rimstone, palustrine, dam, cascade and slope facies. A relationship was inferred between the age of the tufas and the radar signature, in terms of relative amplitude and signal attenuation. Older dry tufas with advanced diagenesis and karstification are characterized by well-defined GPR reflectors and lower attenuation than younger tufas, associated with aquifer discharge and shallower water tables. U-series and radiocarbon ages obtained from the Basturs Lakes tufas indicate that these have been active since 106 ka BP during both cold and mild Marine Isotopic Stages (MIS). We hypothesize that tufas related to the deep-seated Areny-Montsec confined karst aquifer were insensitive to climate variations. Landforms reminiscent of the ITMC have been detected during the last decade on Mars. Since GPR will be part of the ExoMars Rover of the European Space Agency (ESA) mission projected for 2018, we anticipate that our results may be able to constrain the interpretation of landforms possibly related to water on Mars.

ExoMars Rover PanCam: Autonomous & Computational Intelligence [Application Notes

As a part of the Aurora programme for Mars exploration, funded by the United Kingdom Space Agency (UKSA) and European Space Agency (ESA), the UK contributes to the Exobiology on Mars (ExoMars) rover science and engineering programme, with a scheduled launch in 2018; Hence, our Panoramic Camera (PanCam) [9][15] research and development (R&D) is timely. PanCam consists of two stereo Wide Angle Cameras (WAC) and one High Resolution Camera (HRC). While the development is still ongoing, we used funding awarded by the University College London (UCL) Graduate School to conduct investigations in the Himalayas and at Mount Everest Base Camp (EBC), according to the ExoMars rover Reference Surface Mission (RSM). The investigations included capturing stereo and high resolution images using stereo WAC emulators and HRC emulator at altitudes 3490 m, 5150 m and above. Images from different WAC filters, and color images from HRC were acquired at various Pan and Tilt Unit (PTU) mast positions. Our investigation results show significant reduction in data volume with minimum loss in image quality. Furthermore, we introduce a novel autonomous and computational intelligent system called Mission-Specific Data Processor (MSDP) for the rover. It includes Pan-Cam, Visual Data Fusion (VDF), Learning-enabled Object Detection (LOD), Self-Learning Agent (SLA) [22], and Environment Model Library (EML) as part of the rover's computational intelligence [7].

Raman Spectroscopic Analysis of Geological and Biogeological Specimens of Relevance to the ExoMars Mission

A novel miniaturized Raman spectrometer is scheduled to fly as part of the analytical instrumentation package on an ESA remote robotic lander in the ESA/Roscosmos ExoMars mission to search for evidence for extant or extinct life on Mars in 2018. The Raman spectrometer will be part of the first-pass analytical stage of the sampling procedure, following detailed surface examination by the PanCam scanning camera unit on the ExoMars rover vehicle. The requirements of the analytical protocol are stringent and critical; this study represents a laboratory blind interrogation of specimens that form a list of materials that are of relevance to martian exploration and at this stage simulates a test of current laboratory instrumentation to highlight the Raman technique strengths and possible weaknesses that may be encountered in practice on the martian surface and from which future studies could be formulated. In this preliminary exercise, some 10 samples that are considered terrestrial representatives of the mineralogy and possible biogeologically modified structures that may be identified on Mars have been examined with Raman spectroscopy, and conclusions have been drawn about the viability of the unambiguous spectral identification of biomolecular life signatures. It is concluded that the Raman spectroscopic technique does indeed demonstrate the capability to identify biomolecular signatures and the mineralogy in real-world terrestrial samples with a very high degree of success without any preconception being made about their origin and classification.

NIR reflectance hyperspectral microscopy for planetary science: Application to the MicrOmega instrument

Hyperspectral microscopy, by its capability to characterize in situ the composition of samples at their grain size scale and the coupling between the different phases, complements efficiently the remote sensing hyperspectral imagers. Objectives, rationale and limits of hyperspectral microscopy in the planetary science field are summarized in this paper. A new concept of NIR reflectance hyperspectral microscope, MicrOmega is presented and results obtained both with a representative breadboard and a first version of the MicrOmega instrument, recently integrated on the Phobos Grunt lander, are discussed.Results show that we are now able to build instruments capable of analyzing samples at the grain scale, typically a few tens of microns per pixel, within volume, weight, power and time budgets compatible with typical rover’s constraints. We demonstrate the ability of such instruments to characterize samples, identify their major and minor constituents, some non-detectable from orbit, and their spatial coupling.Instruments based on the MicrOmega concept have been selected as part of the Hayabusa-2 Mascot Lander that will study in situ a C-class asteroid, as well as of the ExoMars rover that would characterize Mars potential past and present habitability. In both cases, these in situ analyses should provide essential data to improve our understanding of the history of the object explored.

Effects of Simulated Space Radiation on Immunoassay Components for Life-Detection Experiments in Planetary Exploration Missions

The Life Marker Chip (LMC) instrument is part of the proposed payload on the ESA ExoMars rover that is scheduled for launch in 2018. The LMC will use antibody-based assays to detect molecular signatures of life in samples obtained from the shallow subsurface of Mars. For the LMC antibodies, the ability to resist inactivation due to space particle radiation (both in transit and on the surface of Mars) will therefore be a prerequisite. The proton and neutron components of the mission radiation environment are those that are expected to have the dominant effect on the operation of the LMC. Modeling of the radiation environment for a mission to Mars led to the calculation of nominal mission fluences for proton and neutron radiation. Various combinations and multiples of these values were used to demonstrate the effects of radiation on antibody activity, primarily at the radiation levels envisaged for the ExoMars mission as well as at much higher levels. Five antibodies were freeze-dried in a variety of protective molecular matrices and were exposed to various radiation conditions generated at a cyclotron facility. After exposure, the antibodies' ability to bind to their respective antigens was assessed and found to be unaffected by ExoMars mission level radiation doses. These experiments indicated that the expected radiation environment of a Mars mission does not pose a significant risk to antibodies packaged in the form anticipated for the LMC instrument.

Lunar PanCam: Adapting ExoMars PanCam for the ESA Lunar Lander

A scientific camera system would provide valuable geological context from the surface for lunar lander missions. Here, we describe the PanCam instrument from the ESA ExoMars rover and its possible adaptation for the proposed ESA lunar lander. The scientific objectives of the ESA ExoMars rover are designed to answer several key questions in the search for life on Mars. The ExoMars PanCam instrument will set the geological and morphological context for that mission. We describe the PanCam scientific objectives in geology, and atmospheric science, and 3D vision objectives. We also describe the design of PanCam, which includes a stereo pair of Wide Angle Cameras (WACs), each of which has a filter wheel, and a High Resolution Camera for close up investigations. The cameras are housed in an optical bench (OB) and electrical interface is provided via the PanCam Interface Unit (PIU). Additional hardware items include a PanCam Calibration Target (PCT). We also briefly discuss some PanCam testing during field trials. In addition, we examine how such a ‘Lunar PanCam’ could be adapted for use on the Lunar surface on the proposed ESA lunar lander.

Selecting the geology filter wavelengths for the ExoMars Panoramic Camera instrument

The Panoramic Camera (PanCam) instrument will provide surface remote sensing data for the ExoMars mission. A combination of wide-angle stereo, multispectral, and high resolution imagery will generate contextual geological information to help inform which scientific targets should be selected for drilling and analysis. One component of the PanCam dataset is narrowband multispectral imaging in the visible to near infrared, which utilises a dedicated set of 12 “geology” filters of predetermined wavelength and bandwidth to view the terrain, and provide information on composition and putative mineralogy. The centre wavelengths and bandwidths of these filters were optimised to account for the highly diverse mineralogical terrains the ExoMars rover will hopefully encounter. Six new alternative test filter sets were created, each optimised for the detection of either: sulfates, phyllosilicates, ferric oxides, mafic silicates, iron absorptions, and minor hydration absorptions. These six filter sets were cross-tested using database mineral reflectance spectra and Mars analogue rock multispectral data to find the best performing filter set. Once selected, the bandwidths of this filter set were also optimised. The filter set optimised to ferric oxide minerals was able to most accurately represent rock multispectral data, as well as capture subtle spectral features of hydrated minerals, including sulfates, phyllosilicates, and carbonates. These filters differ from those used on past missions (e.g., Pathfinder, Mars Exploration Rover) and represent the next evolutionary stage in PanCam instrument development. When compared to past filter sets, the updated ExoMars filters capture rock and mineral spectral data more effectively, enhancing the ability of the ExoMars PanCam to detect lithological and compositional variation within an outcrop.

Destruction of Raman biosignatures by ionising radiation and the implications for life detection on Mars

Raman spectroscopy has proven to be a very effective approach for the detection of microorganisms colonising hostile environments on Earth. The ExoMars rover, due for launch in 2018, will carry a Raman laser spectrometer to analyse samples of the martian subsurface collected by the probe's 2-m drill in a search for similar biosignatures. The martian surface is unprotected from the flux of cosmic rays, an ionising radiation field that will degrade organic molecules and so diminish and distort the detectable Raman signature of potential martian microbial life. This study employs Raman spectroscopy to analyse samples of two model organisms, the cyanobacterium Synechocystis sp. PCC 6803 and the extremely radiation resistant polyextremophile Deinococcus radiodurans, that have been exposed to increasing doses of ionising radiation. The three most prominent peaks in the Raman spectra are from cellular carotenoids: deinoxanthin in D. radiodurans and β-carotene in Synechocystis. The degradative effect of ionising radiation is clearly seen, with significant diminishment of carotenoid spectral peak heights after 15 kGy and complete erasure of Raman biosignatures by 150 kGy of ionising radiation. The Raman signal of carotenoid in D. radiodurans diminishes more rapidly than that of Synechocystis, believed to be due to deinoxanthin acting as a superior scavenger of radiolytically produced reactive oxygen species, and so being destroyed more quickly than the less efficient antioxidant β-carotene. This study highlights the necessity for further experimental work on the manner and rate of degradation of Raman biosignatures by ionising radiation, as this is of prime importance for the successful detection of microbial life in the martian near subsurface.

GPR detectability of rocks in a Martian-like shallow subsoil: A numerical approach

In this work, the ability of Ground Penetrating Radar (GPR) to detect rocks buried in composite soil is studied in connection with the planned ExoMars mission, as GPR will be used during this mission to scan the Martian subsurface to help define feasible sites for shallow drilling. A realistic model of the operating environment is implemented through a full-wave electromagnetic simulator, taking into account the antenna system and the signal features. The flexibility and efficiency of this numerical approach has allowed for the analysis of a great variety of configurations. The regolith is modeled based on data from recent explorations, while various kinds of embedded rocks are considered that have different geometrical and physical characteristics. The simulated results are compared with ad hoc GPR measurements performed on basalts buried in a mixture of glass beads, as an analogue of a dry sandy Martian soil. A very good agreement between theoretical and experimental results is found, thus validating the proposed numerical approach. This research has defined useful and reliable information concerning the prediction of scattering effects from buried objects in the environment where the ExoMars rover will operate.

Characterisation of martian soil simulants for the ExoMars rover testbed

The European Space Agency (ESA) ExoMars mission involves landing a rover on the surface of Mars on an exobiology mission to extend the search for life. The locomotion capabilities of the ExoMars rover will enable it to use its scientific instruments in a wide variety of locations. Before it is sent to Mars, this locomotion system must be tested and its performance limitations understood. To test the locomotion performance of the ExoMars rover, three martian regolith simulants were selected: a fine dust analogue, a fine Aeolian sand analogue, and a coarse sand analogue. To predict the performance of the ExoMars rover locomotion system in these three regolith simulants, it is necessary to measure some fundamental macroscopic properties of the materials: cohesion, friction angle, and various bearing capacity constants. This paper presents the tests conducted to determine these properties. During these tests, emphasis was placed on preparing the regolith simulants at different levels of density in order to evaluate its impact on the value of the parameters in particular. It was shown that compaction can influence the Bekker coefficients of pressure-sinkage. The shear properties are consistent with the critical state model at normal stresses similar to those of the ExoMars rover in all but one of the simulants, which showed behaviour more consistent with transitional soil behaviour. It is necessary to give due consideration to these variations to ensure a robust test regime is developed when testing the tractive ability of the ExoMars mobility system.