Hydro-Morphodynamic Delta Modelling for Future Exploration Insights at Oxia Planum, Mars

The European Space Agency (ESA) plans to launch the Rosalind Franklin rover in 2028. The aim of this mission is to search for biosignatures and to investigate Oxia Planum (Altieri et al., 2023). This landing site was chosen because it is one of the oldest Noachian terrains (4-3.6 Ga) altered by water, yet logistically feasible for landing and roving. Oxia Planum is rich in clays, hydrated minerals, suggesting the past influence of liquid water (Mandon et al., 2021). A river delta has been identified close to the landing site at the termination of Coogoon Vallis (Quantin-Nataf et al., 2021). The delta presents potential for preserving biosignatures either by covering underlying clays or in within its own deposits, providing protection from radiation and oxidation. Despite knowing that water played an important role at Oxia Planum, it is still unclear what the past fluvial and environmental conditions were like.

Deltas on Mars are important targets for planetary exploration due to their indicators of past fluvial activity, contain a sedimentary record available to study, and have potential for preserving past signs of life. The observable delta deposits, captured by satellite and rover imagery, serve as key sources for deducing ancient fluvial and climatic conditions on Mars (e.g. Salese et al., 2020; Toffoli et al., 2021; Mangold et al., 2021). This study will use the observed river delta at Oxia Planum to investigate past fluvial and environmental conditions at the landing site. Specifically, this study aims to constrain the range of possible hydrological conditions in terms of duration of activity, flow energy conditions and water levels. These insights contribute to the strategic planning of the rover mission, aiding in the identification of drilling locations of interest.

To investigate the Oxia Planum delta, we developed a 2D-horizontal hydro-morphological model. We used the numerical modelling software package Delft3D FM (by Deltares), which was amended for Martian gravity. We explored multiple scenarios including, different water levels in the basin, river discharges, sediment supply rates and grain sizes. Some scenarios aimed to replicate the final phase of delta activity, while others sought to reconstruct the evolution of older delta lobes. Although the preliminary results are subject to ongoing investigation, they hold promise for refining estimates (both lower and upper bounds) of fluvial conditions such as discharge, water level, sediment transport rates, morphological development, and duration of activity. Given the distinct sediment transport dynamics on Mars due to lower gravity (Braat et al., 2023), reliance on investigative modelling becomes imperative, as the direct use of Earth analogues is challenging.