The uncertainty of science: A new review of data from Curiosity now suggests that Gale Crater was not filled with a lake in the past — as generally believed — but instead simply had small ponds on its floor.
Previous analyses of data from Curiosity have relied heavily on a measure called the chemical index of alteration to determine how rocks were weathered over time. Joseph Michalski at the University of Hong Kong and his colleagues have suggested that because this measure was developed for use on Earth, it may not be valid in the extreme Martian climate.
Instead, they analysed the concentrations of various compounds that are expected to change based on different types of weathering over time. They found that some of the layers of rock Curiosity examined did interact with water at some point in their past, but more are likely to have formed outside of the water. “Over hundreds of metres of strata, it seems that the only layers that are demonstrably lacustrine [formed in a lake] are the lower few metres,” says Michalski. “Of the rocks visited by the rover… the fraction that is demonstrably lacustrine is something like 1 per cent.”
These rocks were mostly in the lowest few metres of sediments in the crater, suggesting the lake was not nearly as deep or extensive as we thought. “There was likely a small lake or more likely a series of small lakes in the floor of Gale crater, but these were shallow ponds,” says Michalski.
This conclusion also aligns with other recent work proposing that Gale Crater was always cold and never had running water.
None of this is proven, one way or the other, though this new conclusion would make it easier to explain Mars entire geological history. Trying to create models for Mars’ past climate that allowed large amounts of liquid water on its surface have so far been difficult at best, and have generally been unconvincing. Eliminating the need for liquid water will make explaining Mars’ geology much simpler.
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