Sandstone outcrops seen with the ExoMars PanCam emulator

Post by Dr. Peter Fawdon, (@DrPfawdon) School of Physical Sciences, The Open University, United Kingdom

PanCam (Coates et al., 2017) is the imaging instrument on the 2020 ExoMars rover and consists of two wide angle cameras; (WAC’s) and a High Resolution Camera (HRC). PanCam will be used to lead the geological characterisation of the local area outcrops. It will be used to establishing the geological setting of outcrops and identify targets for subsurface sampling and analysis with the ExoMars drill and suite of analytical instruments (Vago et al., 2017).

An emulator for the ExoMars PanCam instrument has been used in rover operation field trials in southern Spain. The aim of these trials has been to explore how scientists will use the instruments in rover missions. These images, taken by the emulator, are examples of what PanCam data might look like and show how the PanCam images will be used (e.g., Harris et al., 2015).

Picture1

Image 1: PanCam Multi-spectral images: (A) A colour composite made from the red, green and blue filters shows a ridge named ‘Glengoyne’ at approximately 20 m distance from the rover. (B) A Multi spectral image using the geology filters stretched to emphasise the variation in the scene.

During the rover trial PanCam’s WAC’s were used to identify outcrops of interest from a distance. Image 1 shows a low ridge (~50 cm high) cropping out of a smooth gravel plain close to the rovers starting location. This outcrop was initially identified in the 360° panoramas and called ‘Glengoyne’. Image 1 was taken after the rover moved around the outcrop and this colour image was used to make an initial geological characterisation of the ridge. The upper part of the ridge, called the Glengoyne member, is made of a dark brown material that is more resistant to erosion than the lower part of the ridge. It appears to vary in thickness and stereo data showed that this unit dips away from the camera. The lower part of the ridge, called the Keele member is pale grey green in colour and a decorrelation stretch made using data from the PanCam geology filters (Cousins et al., 2012) suggests layered variations, picked out in the red and green end members.

Picture2

Image 2: Targeting and HRC images of the Keele member: A section of a panoramic PanCam image (A) taken at the end of a drive used to target HRC data to be collected on the next sol (Martian day). (B) HRC image of the Keele member from a distance of ~4 m showing variation in the colour and texture of the surface.

The HRC was used both at long range, to build a picture of the context around the Glengoyne ridge, and at close range, to look at details in the outcrop. Image 2 shows how the panoramic images taken at the end of a drive are used to select targets for the next day’s imaging operations. The first image (2A) was taken at the end of a day and shows the crest of the westerly dipping Glengoyne ridge overshadowing the keel member, this relationship implies that the Keele member is made of a softer lithology and is more susceptible to erosion. This was chosen as an area of interest and used for targeting images in rover operations the following day. Image 2B shows the HRC image taken the following morning in more favourable lighting conditions. This shows that Keele Member has both pale greenish grey and reddish brown regions – likely associated with variation in oxidation state of Iron minerals, with some irregular light toned clasts. The image also shows a patchy white surface coating, possibly made of evaporate minerals.

From these observations, and further observations of the Glengoyne member with the HRC and close up imagers (CLUPI) (Josset et al., 2017) it was hypothesized that this outcrop represents a sandy mudstone, rich in evaporate minerals, likely gypsum and halite, that was cut down into by a shallow channel sandstone before further burial lithification and exposure. This is one of the geological settings we would hope to explore with the ExoMars rover in 2020 because, on the Earth, a depositional environment such as this would make a good location for the preservation of biomarkers. Central to the mission goal of the ExoMars rover which is to search for signs of past and present life on Mars and to characterise the water/geochemical environment as a function of depth in the shallow subsurface.

Further Reading

Vago, Jorge L., et al. “Habitability on early Mars and the search for biosignatures with the ExoMars Rover.” Astrobiology 17.6-7 (2017): 471-510.

Coates, A. J., et al. “The PanCam instrument for the ExoMars rover.” Astrobiology 17.6-7 (2017): 511-541. Gelogical filters

Cousins, Claire R., et al. “Selecting the geology filter wavelengths for the ExoMars Panoramic Camera instrument.” Planetary and Space Science 71.1 (2012): 80-100.

Harris, Jennifer K., et al. “Remote detection of past habitability at Mars-analogue hydrothermal alteration terrains using an ExoMars Panoramic Camera emulator.” Icarus 252 (2015): 284-300.

Josset, Jean-Luc, et al. “The Close-Up Imager onboard the ESA ExoMars Rover: objectives, description, operations, and science validation activities.” Astrobiology 17.6-7 (2017): 595-611.

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