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The tides of Venus

Wrestling some science off of Mars: How clays became sexy.

This side-by-side comparison shows the X-ray diffraction patterns of two different samples collected from the Martian surface by NASA’s Curiosity rover. NASA/JPL-Caltech/Ames

With this picture, clays just became the new sexy science, in mineralogical terms at least (well having said that if you’re into mud wrestling then I suppose clays have long been sexy). Here is the long-sought confirmation, from NASA’s Curiosity rover, that there are indeed clays on Mars. But what’s all the fuss about? We’ve loads of clay here on Earth, both on and off the mud wrestling arenas of the world, why has finding them on Mars got everybody so excited?

Well first it’s a nice bit of proof that geological processes have happened on the Martian surface, it’s not just red and dead. Clays only form as alterations products when a liquid (usually that is slightly acidic) has long-term contact with a rock. Over time this liquid eats into the rock and changes its crystal structure. This is what the picture that the CheMin team put out is showing; along with the parent rock (mainly basalt) they are finding this other pattern from something very different.The alteration processes that make clays are great markers on what sort of temperatures and climate conditions were around at the time. So by closely examining the end product, the clay, we can get an idea of what sort of weather was about earlier in Martian history.

Unlike the rocks they are altered from, clays are really light and mobile. On Earth we see that they can be picked up by wind and water and transported many thousands of miles. Has this been the case on Mars? Very early days, but if the Mars rover can show that the clays are not quite where they used to be, then that begins to paint a pretty dynamic picture of the Martian surface. This is not pure speculation, in fact one of the reasons that the Spirit and Opportunity rovers lasted as long as they did was because their solar panels regularly got swept clean by the winds of Mars.

Dust devils on Mars as captured by the HIRISE orbiter.

But all of this raises the excellent point, where are all these liquids now? Looking over abstracts for the on-going Lunar and Planetary Science conference over in Huston, this is very much an ongoing research area. Data from the Curiosity rover’s suite of instruments has already provided a number of clues to this. But it how the data these instruments collect will change as the rover progresses up Mt Sharp that will help the most.

A mosaic of images from the Mast Camera (Mastcam) on NASA’s Mars rover Curiosity, which shows Mount Sharp in a white-balanced color adjustment that makes the sky look overly blue but shows the terrain as if under Earth-like lighting. NASA/JPL-Caltech/MSSS

Curiosity is currently sitting at the bottom of this imposing feature, which is thought to be a giant layer cake built upof material deposited over time. As the rover it trundles up its slopes it will travel forward in time and see the changes in the materials. If one layer does not have clays, but the next one above it does, that will start to paint a picture of how Mars may have changed back and forth from being warm and wet to being cold and dry. If however there’s a big change with no clays above a certain point, then we’ll have a clue that Mars’s climate in the past would have just changed the once from being warm and wet, to how we know it today.

As with every good bit of science, the discovery of clays on the Martian surfaces raises more questions that it answers. But if you examine the building blocks that make up clays, there may be a further surprise in store.

Clay minerals are made up from layers of silicate (silicon and oxygen) and layers of metal oxide, which are sandwiched together with water. They are part of a group of layered silicate minerals, called phyllosilicates, which now I think of it must be where the term filo or phyllo pastry comes from. These layers can swell up and take in many things from their surroundings.

Clays in a more terrestrial use. Flickr/alli

That’s why we (well us ladies at least) put clays on our faces as face masks. The clay grabs the moisture from our skin and sucks it in, along with all the grub and grime on our skin. The layers within clays also make them very soft and slippery, which is why they are nice to put on your skin and are the main type of ‘mud’ used in mud wrestling.

This ability to suck up moisture and other bits make clays a super place to live if you’re a small microbe. You’ve access to water, food and a snug place to live. It’s an intriguing prospect, and sadly Curiosity doesn’t have the instruments to tell us if this is happening.

Have I achieved the impossible? Have I convinced you all that clays are really quite sexy, and that there’s a ton of science to be done with them, both on and off Earth? Whatever the effect, I reckon that you’ll never think of mud wrestling in quite the same way again.

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