The Mars Rover Curiosity has been finding many rocks rich in silica, a compound formed from silicon and oxygen, in an area of ​​Mount Sharp on Mars that it’s been exploring for some months. A few months ago the discovery of that kind of rocks was a surprise, so much so that mission managers changed the Curiosity’s research schedule to perform further analyzes. That decision led to the discovery of other silica-rick rocks and to further studies to try to explain their presence.

The presence of all that silica is surprising because of the possible ways in which such an amount can be formed. One way consists in the separation of one or more soluble components from a solid mass by means of an acid, a process technically called leaching. A substance that can cause this reaction is acidic water while water that is neutral or is containing substances that make it alkaline can carry dissolved silica that would be deposited from the solution.

In essence, the presence of water in the area may have been decisive to form a silica concentration never seen so far on Mars. In some rocks, silica makes up even 90% of their composition. The consequence is that there may be entire blocks of quartz, one of the minerals that on Earth are common forms of silica.

In the past, the Mars Rover Spirit detected signs of sulfuric acidity in an area very far from Mount Sharp. This adds still other possibilities of silica formation. The last months of analyzes have been providing very few certainties that are surprising and consequently many questions.

The Mars Rover Curiosity started finding significant amounts of silica in the rocks of the area called “Marias Pass” and again in September and October in the area called “Bridger Basin”. The distance between the two areas is a few hundred meters (about a third of a mile) and this means that silica is abundant in a wide area.

In these areas several rocks were analyzed using various instruments of the Mars Rover Curiosity. The measurements made by the Chemistry & Camera (ChemCam) and Dynamic Albedo of Neutrons (DAN) instruments were followed by more detailed studies carried out with the APXS (Alpha Particle X-ray Spectrometer) spectrometer and the MAHLI (Mars Hand Lens Imager) camera.

The mystery is made even more complex by the discovery of a form of silica called tridymite, a silicon dioxide. On Earth tridymite is rare and is found in recent volcanic rocks, which is formed due to high temperatures. The Mars Rover Curiosity instead found tridymite in the area called “Marias Pass” that is believed to have been formed by deposits on an ancient lakebed.

On Earth, volcanic magma can evolve becoming silica-rich. It’s possible that on Mars there’s been a similar phenomenon leading to the formation of tridymite as well. The presence of silica is connected to the geological history of the area so this study quickly became a priority and will keep on being pursued.

When silica-rich rocks were discovered for the first time Roger Wiens from the Los Alamos National Laboratory, the principal investigator of the ChemCam instrument, pointed out that one never knows what to expect on Mars. His words were confirmed with the discovery of an area that is very different from anything that the Mars Rover Curiosity had found in the first two years of its mission.

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