Modelling the history of water in the Jezero crater

Jezero crater, which once contained a paleolake, is the investigation site of the current NASA's Mars 2020 mission. We modelled 9 water related processes in Jezero: 1) western inlet valley carving, 2) northern inlet valley carving, 3) crater flooding by only northern inlet and 4) by both northern and western inlets, 5) erosion of the eastern rim for the outlet, 6) water outflow from the crater, 7) outlet valley carving, 8) western delta deposition, 9) northern delta deposition. We claim that the northern inlet had participated in the crater flooding because it has terraces at the same height level as the breaching terraces in the outlet (breaching happened in 3 phases, as shown in [1]).

Measurements of channel sizes, valleys, deltas, eroded rim and outflowed water volumes were conducted in ArcGIS 10.8 using Mars 2020 Science Investigation CTX DEM Mosaic and HRSC Mars Chart DTM and corresponding ortho-mosaics.

We used flow discharge and sediment transport models by [2] to calculate minimum water and sediment transport timescales under constant bank-full discharge. For northern and western inlet-related processes we took 0.005 m as median grain size D50 (it is the biggest grain size reported for samples from the western delta front in [3] so far; considering that the delta front is characterized by fine-grained deposition, it is reasonable to assume that for the whole delta D50 could be equal and even exceed 0.005 m). For outlet and breaching-related processes we used 0.1 m as D50 (which is used to model breaching events, e.g. in [1] and [4]).

Various scenarios have been modelled; the most probable (according to our current knowledge) were analyzed.

Deposition of the deltas could happen simultaneously with the last incision of corresponding valleys; the amount of carved material from last incised valleys is approximately the same as deposited in deltas.

According to the modelled scenario, the eastern rim erosion lasts five times longer than the water outflow after breaching. This indicates that water discharged from the breach could not alone erode the rim and thus more water supply from inlets would be needed. However, the uncertainty of grain size calls this result into question.

Another conclusion is that the northern valley alone could provide enough water (~1000 km³) during its last incision to fill the crater before breaching (446 km³). Moreover, the last incised valleys were mostly carved after the breach; if not, they would have already provided enough water to fill the crater and the breaching would have already happened.

Comparison of water discharged after the breach (238 km³) with water needed to carve at least the last incision outlet valley (~4000 km³) shows that Jezero had to be an open-basin lake after breaching.

 

References:

[1] Salese, F. et al. (2020). Astrobiology, 20(8), 977–993.

[2] Kleinhans, M. G. (2005). Journal of Geophysical Research: Planets, 110(12), 1–23.

[3] Farley K., and Stack K. (February 15, 2023). Mars 2020 reports, Volume 2 - https://mars.nasa.gov/internal_resources/1656/

[4] Roda, M. et al. (2014). Icarus, 236, 104–121.