Water – the most important prerequisite for life
Jezero crater is a Noachian crater that once contained a paleolake and deltas (marked as lacustrine fan delta = LFD) that were fed by large regional watersheds. Two inlet valleys can be spotted in the northern and northeastern part of the crater. The HRSC map clearly shows a much smoother topography of the northern part of the crater floor compared to the much steeper crater rims in the southern part. Materials eroded from the large catchment area north of the crater were transported and deposited inside Jezero, building up the deltas and smoothing out the floor. A large outlet channel is located at the eastern part of the crater and shows a swell at the rim of the crater. This means that there must have been a relatively constant supply of water into the crater to carve such a large outlet valley and that some water always remained behind the swell, in the crater lake. This is very well visible in the profiles starting with the inlet channels (In1 and In2), merging in the central basin, passing over the swell into the outlet channel (Out1).
The floor of Jezero crater has an elevation of 2,700 metres below the notional 'sea level' on Mars. Strictly speaking, this reference level, which is used on the map shown here, is a surface of equal gravitational attraction, referred to as an areoid. The lake in Jezero crater is thought to have been at least 250 metres deep (with a size of approximately 1,340 km²), a figure derived from the altitude measurements for the crater rim, the crater floor, the river valley profile and the upper edges of the deltas. However, it is no longer possible to make precise estimates today, as the deltas have been severely eroded since water activity ceased approximately 3.8 billion years ago. In addition, the crater was filled with very extensive lava flows from the nearby Syrtis Major region about 300 million years later.
The topographical map clearly shows how the northern part of the crater floor is sloping and this results in a less clearly defined crater rim when compared to the flat, southern part of the crater floor and the steeper southern flanks. This is due to the erosion of material in the catchment areas to the north of the crater, which was then transported into the crater itself and deposited as sediments in the delta. The erosion of the northern crater rim by the three river valleys that break through it also contributed to the creation of Jezero's asymmetrical topography.
Clay minerals, particularly carbonates, which have been discovered in comparatively large quantities in the western delta, are significant as potential repositories of biosignatures – that is, traces of microbial life. The early presence of liquid water and the enormous carbonate deposits here make Jezero a perfect destination for the search for possible past life on Mars.