Curiosity Mars rover – on the prowl since August 2012.
Credit: NASA/JPL-Caltech/MSSS

NASA’s Curiosity Mars rover is now in Sol 2193.

The last images from the Mars machinery reached Earth back on Sol 2172, September 15th.

Engineers continue to wrestle with a glitch that prevents Curiosity from sending science and engineering data stored in its memory.

According to the Jet Propulsion Laboratory, the robot remains in its normal mode “and is otherwise healthy and responsive,” reported Ashwin Vasavada, the Mars Science Laboratory’s project scientist at JPL back on September 19th.

Geological crime scene

Meanwhile, in a new geological update from Susanne Schwenzer, a planetary geologist at The Open University in the United Kingdom: “Geology…it’s like investigating a crime scene.”

“Sometimes planetary geology is like forensics,” Schwenzer says. “We are presented with a crime scene: Something broke down the original igneous rock, and made all those clays, veins and hematite nodules. We know this something was a fluid, but in order to find out exactly what has happened, we need to examine all the evidence we have.”

This view from the Mars Hand Lens Imager (MAHLI) on the arm of NASA’s Curiosity Mars rover shows a combination of dark and light material within a mineral vein at a site called “Garden City” on lower Mount Sharp. The image was taken on April 4, 2015, and covers an area roughly 1 inch wide.
Credit: NASA/JPL-Caltech/MSSS

That often starts with investigating the Curiosity images, and in great detail. Mastcam images for the geologic context, then Remote Micro Imager (RMI) photos and/or the Mars Hand Lens Imager (MAHLI) for the close-up details. But what about the chemistry?

Minerals with water

“We are a small team here in the UK, specializing in what is called “thermochemical modelling.” Thermochemical modelling uses mathematical equations that are based on known reactions of minerals with water,” Schwenzer explains. “The models combine many thousands of such reactions into equations, which can be solved iteratively to arrive at a reaction path for a known rock composition. And once we determine what reacted and how, we can also infer which chemical elements remained in the water because they were not included in the reaction products.”

In other words, Schwenzer adds, scientists can find out how the chemical elements are distributed between the fluid and the newly forming minerals. “Some of our French and American colleagues use this method too, and we always have great discussions to advance our work.”

Clays and veins

All the data — images and chemistry from Chemistry and Camera (ChemCam) and the Alpha Particle X-Ray Spectrometer (APXS) – is studied, and where available also mineralogy from the rover’s Chemistry & Mineralogy X-Ray Diffraction/X-Ray Fluorescence Instrument (CheMin).

“That’s the evidence at our crime scene,” Schwenzer adds. “But who broke the rock and left all those clays and white veins?”

We know it is “the fluid,” and the modelling allows us to find out what temperature and composition this fluid might have had, Schwenzer points out. “For example, we have looked at the veins Curiosity found very early in the mission – at Yellowknife Bay. They were very pure calcium-sulfate, especially compared to what Curiosity measured later at Garden City and now at Vera Rubin Ridge.”

Credit: NASA/JPL

A clue

The purity of the calcium-sulfate at Yellowknife Bay provided a clue:

“If we model a typical Yellowknife Bay rock with all chemical elements in the proportions available in this rock to react with water, then we will get veins that have more than just calcium-sulfate. We would therefore expect veins that have other minerals such as iron oxides and quartz,” Schwenzer reports.

But the veins at Yellowknife Bay did not have any of those additional minerals.

“Therefore, we concluded that they must have come from water selectively dissolving a pre-existing mixed-mineralogy layer,” Schwenzer says. “The dissolution of this pre-existing layer would have left the less soluble minerals – quartz, iron oxides – behind while transporting the calcium and sulfate. This would have allowed the formation of a very pure calcium-sulfate, which is what was observed! But how does that help us at Vera Rubin Ridge?”

Ongoing investigation

Curiosity is positioned now to investigate a very complex area, which has clearly seen the interaction of rocks with fluids.

“There are veins much more complex than the ones at Yellowknife Bay, and in addition there are iron nodules, crystal moulds and color changes,” Schwenzer notes. “We, the modellers, are working hard to understand how the fluid changed to produce all this new evidence… more later, as investigators rarely talk about ongoing investigations, right?”

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