Curiosity was to analyze the Gale Crater on Mars, believed to be an ancient lake. But the NASA rover would rather have found sediment deposited here by the wind, which reveals unexpected secrets.
When the Curiosity rover landing site was chosen, the idea was to analyze what once housed a lake, and therefore find rocks that had been in contact with water. This is what NASA’s little car has done successfully since arriving in Gale Crater in November 2011.
But a study published in Science Advances on August 6 reveals that the rocks that cover the surface of this crater are actually sediments deposited here by the air. It may sound like a disappointment, but not at all! On the contrary, even since certain samples examined by Curiosity and its ChemCam (the ancestor of the SuperCam of Perseverance, both developed by France), are indeed of lake origin. The discovery of other samples from elsewhere is according to the authors of the study: ” uno crucial piece in understanding the puzzle of the global weathering of Mars. “
There is a lake, but …
In reality, rocks that have been formed in an underwater environment, or have been in contact with a large amount of water, for a relatively long time, are quite rare, if not the exception. The vast majority of what forms Gale Crater would actually be a collection of sand and various sediments formed in the open air and later deposited in the dry crater.
The authors write: ” Some samples had been interpreted as lacustrine, but this was via a technique used on Earth that doesn’t apply as well here. This technique, it is called CIA for Chemical index of alteration. This chemical alteration index in French is used to characterize how rocks have been altered by their environment. But while it works well on Earth in well-known environments, it is less the case on Mars under very different conditions. For example, it does not assess alteration by iron and magnesium, rare among us, but abundant on the red planet. No reference either to the acidity of the surface of Mars, nor to calcium and sodium, the amounts of which are not at all the same from one planet to another.
From this premise, the researchers re-analyzed eight years of data acquired by Curiosity to show that the rocks were more likely to have been formed in the open. Their weathering corresponds more to that of a rock subjected to the acidity of the Martian surface and to the elements found there.
“A global process”
They were able to highlight certain minerals that were slightly blue, a sign of iron deficiency. A blue that can be found elsewhere on the planet, especially in Mawrth Vallis, a site also considered for Curiosity, but also in the Martian atmosphere!
” That means, summarize the authors, that the observations of the Gale crater are representative of a global process on a planetary scale. Curiosity did visit a lake, certainly shallower than expected, but found rocks that had stayed underwater. That said, this unexpected discovery of minerals from elsewhere reveals secrets of Mars that Perseverance may shed light on.