Image that Curiosity took from "Old Soaker" during the sun 1555. The slab is about 80 cm long. Photo: NASA
Since the desiccation cracks form only when the moist sediment is exposed to the atmosphere, its position closer to the center of the old lake bed than to the edge also suggests that lake levels increased and declined drastically over time. That is, the lakes of Gale Crater would have gone through the same kind of cycles that we see on Earth.
The researchers focused on a slab of rock the size of a coffee table dubbed "Old Soaker." Old Soaker is crossed by polygons identical in appearance to those characteristic of terrestrial drying processes. The team analyzed the physical and chemical aspects of the polygons using the entire array of Curiosity analysis media. We must remember at this point that Curiosity is a very powerful self-propelled geochemical laboratory.
This scrutiny showed that the polygons, confined to a single layer of rock and with sediments filling the cracks between them, were formed by exposure to the atmosphere, and not by other mechanisms such as thermal or hydraulic fracturing. And while scientists knew almost from the moment that Curiosity landed in 2012 that Gale Crater once contained lakes, the confirmation of the existence of dewatering cracks adds a context to our understanding of this ancient lake system.
Finding after finding, Curiosity is continuously and completely transforming our vision of the present and the past of Mars.
Reference:
N. Stein et al (2018) Desiccation cracks provide evidence of lake drying on Mars, Sutton Island member, Murray formation, Gale Crater Geology doi: 10.1130/G40005.1
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