Adam Parkes Bowen
Following its selection as the landing site for the ExoMars rover “Rosalind Franklin”, the study and mapping of Oxia Planum ahead of its arrival is essential and ongoing. To aid in this effort an analysis of Colour and Stereo Surface Imaging System (CaSSIS) imagery, along with a comparison between fractured terrains at Oxia Planum and Gale Crater, the landing site for the Curiosity rover, are currently underway.
CaSSIS is a high-resolution (4.5 m/pixel) 4-band visible to near-infrared imager. From a study carried out using CaSSIS, along with co-analysis from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and High Resolution Imaging Science Experiment (HiRISE) colour imagery, two spectrally and morphologically distinct subunits of the Oxia clay unit were identified. These were a lower member showing metre-scale fracturing and spectral signatures indicative of Fe/Mg-rich clay minerals, and an upper member showing decametre scale fracturing with Fe/Mg-rich clay mineral/olivine signatures. To expand upon the mapping carried out using HiRISE colour and CRISM data, which was limited by data coverage/resolution, CaSSIS and HiRISE RED i.e. greyscale, imagery was used to identify and map out these sub-units. This is being done to aid future planning of rover traverses to high priority surface targets.
Analysis of fracturing within ancient terrains is potentially a useful tool for determining the history and material properties of a region, as the form a fracture network takes varies depending both on the mechanisms which generated it as well as the materials within which the fracturing occurred. Comparisons between fractured terrains across Oxia, as well as with those at Gale crater due to the “ground truth” provided by the Curiosity rover, are being made. This is done in an effort to predict material properties and the fracture’s formation mechanisms, along with determining how fractures across Oxia relate to one another.
A recent study using Colour and Stereo Surface Imaging System (CaSSIS) data, along with co-analysis from CRISM and HiRISE colour imagery, identified that at least two spectrally and morphologically distinct subunits make up the Oxia clay unit. These were a lower member showing metre-scale fracturing and spectral signatures of Fe/Mg-rich clay minerals, and an upper member showing decametre scale fracturing with Fe/Mg-rich clay mineral/olivine signatures.
This work also showed that ferric detections from band ratioed CaSSIS imagery correlated well with CRISM clay detections and that its two subunits were differentiable by CaSSIS. Following this CaSSIS, in conjunction with HiRISE greyscale imagery, is being used to map these two sub-units. As CaSSIS has a higher resolution at 4.5m/pixel, and will have near 100% coverage of the landing site by the time of the rover’s launch, CaSSIS can be used to improve the resolution and coverage of the Oxia clay map. The current map of the two subunits is shown within the poster, along with two figures comparing a band ratioed CaSSIS (NIR÷BLU, PAN÷BLU, PAN÷NIR) image and 18m/pixel CRISM Fe/Mg clay map of the same section of Oxia. This comparison shows strong agreement between them.
Comparisons between fractured terrains across Oxia with those at Gale crater are also being made. This is done as, depending on their formation mechanism along with the host material, the form a fracture network takes varies. By mapping networks at Oxia, and comparing them to those within the well characterised surface at Gale, we can use our knowledge of Gale to make predictions about Oxia. Mapping was done at a 50x50m scale with length, polygon area and fracture intersection angle being measured. Kernel Density Estimation (KDE) diagrams were used to visually compare the data, while 2-sample Kolmogorov-Smirnov tests were used to determine whether each data set originated from the same population to a 95% level of probability.
Two sites at Gale showed similarities to those at Oxia; one in Sheepbed member at Yellowknife Bay, similar to both a network within Oxia’s clay (OC) unit (designated site 8) and another in an olivine-rich unit (site 9). The other was in Vera Rubin ridge (VRR), comparable to two networks within the OC unit (sites 4/7). The sites that YKB and VRR are comparable to are limited, with the networks not limited to a specific region or what is nominally the same unit, suggesting a more complicated history of Oxia Planum’s clay unit than CRISM and OMEGA maps would indicate; in what way is still being determined
Intra Oxia comparison shows two groupings; two networks in the clay unit, sites 7/8, located near a large capping unit exposure, and site OC1 and site 9, adjacent to a large delta fan. OC7/8 are dissimilar to the other networks, with the exception of OC4 being comparable to OC7. Given the similarity with OC4, located tens of kilometers away, this indicates whatever caused OC7/8 to differ from the other networks isn’t due to geographical separation. Further work must be done to determine what this was.
OC1/9 both have very similar metric distributions and are distinct to those seen elsewhere at the site. Given their location and strong differences compared to other networks, it is likely the event which formed them was linked or influenced by the emplacement of the delta; further work is needed to confirm this.