How vanadium could be a beacon for Martian life

How vanadium could be a beacon...
An artist's rendering of the Mars 2020 rover on the surface of the Red Planet
An artist's rendering of the Mars 2020 rover on the surface of the Red Planet
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An artist's rendering of the Mars 2020 rover on the surface of the Red Planet
An artist's rendering of the Mars 2020 rover on the surface of the Red Planet

If all goes according to plan, in 2020 NASA (in addition to several other space agencies) will launch a rover towards Mars. When it lands there, it will begin looking for signs of past or present life on the Red Planet. To help astrobiologists tease out biological material from other deceiving compounds in the planet's regolith, researchers at the University of Kansas (KU) suggest focussing efforts on finding the element vanadium.

Right now there are five space organizations set to launch rovers to Mars in 2020, to take advantage of the relatively close proximity of the planet to Earth at that time. Among those will be both the Mars 2020 rover from NASA and the ExoMars rover from the European Space Agency. Chief among these missions will be the hunt for both the conditions for life to exist on Mars or evidence of life itself – either currently or in the past.

In terms of seeking out previous life, astrobiologists analyzing the findings of the rovers will focus, in part, on the fossilized remains of ancient Martian microorganisms. They'll do this by looking for carbon in the soil samples through a process known as Raman spectroscopy, which measures the vibrations and therefore composition of molecules by examining the way light (such as that from a laser) scatters when it hits a sample. But, the KU researchers say, this method is far from foolproof.

"People say, 'If it looks like life and has a Raman signal of carbon, then we have life,'" said Craig Marshall, the lead author of a paper on the findings published in the journal Astrobiology and an associate professor of geology at the University of Kansas. "But, of course, we know there can be carbonaceous materials made in other processes – like in hydrothermal vents – consistent with looking like microfossils that also have some carbon signal. People also make wonderful carbon structures artificially that look like microfossils – exactly the same. So, we're at a juncture now where it's really hard to tell if there's life only based on morphology and Raman spectroscopy."

So Marshall and his team recommend a different approach: using a process called X-ray fluorescence microscopy to seek out the element vanadium in samples. This process relies on reading the results that come back to a monitor after a test sample is bombarded with X-rays, and NASA's rover will have the proper equipment on board to conduct such tests. Using it to look for vanadium, they say, will result in a more accurate idea of whether the sample under question did indeed come from a long-ago microorganism.

That's because vanadium is often left behind in substances formed from biological samples. On Earth, for example, it occurs in crude oil and black shale. Vanadium also tends to worm its way into biological samples through its entanglement with chlorophyll.

A tangled mess

"Vanadium gets complexed in the chlorophyll molecule," Marshall said. "Chlorophylls typically have magnesium at the center – under burial, vanadium replaces the magnesium. The chlorophyll molecule gets entangled within the carbonaceous material, thus preserving the vanadium.

"It's like if you have a rope stored in your garage and before you put it away you wrap it so you can unravel it the next time you need it. But over time on the garage floor it becomes tangled, things get caught in it. Even when you shake that rope hard, things don't come out. It's a tangled mess. Similarly, if you look at carbonaceous material there's a tangled mess of sheets of carbon and you've got the vanadium mixed in."

To see if their process works, the team tested it on Earth-based microfossils called acritarchs, which might be similar to the remains of ancient life we could find on Mars. Sure enough, the samples analyzed by the team contained the vanadium they expected to find.

"We tested acritarchs to do a proof-of-concept on a microfossil where there's no shadow of a doubt that we're looking at preserved ancient biology," Marshall said. "The age of this microfossil we think is Devonian. These guys are aquatic microorganisms — they're thought to be microalgae, a eukaryotic cell, more advanced than bacterial. We found the vanadium content you'd expect in cyanobacterial material."

NASA is also currently testing equipment for finding life by using Earth-based samples from the Atacama desert in Chile. Marshall hopes the new vanadium-based technique will help further future efforts.

"Hopefully someone at NASA reads the paper," said Marshall. "Interestingly enough, the scientist who is lead primary investigator for the X-ray spectrometer for the space probe – they call it the PIXL – was his first graduate student from Macquarie University, before his KU times. I think I'll email her the paper and say, 'This might be of interest.'"

Source: Kansas University

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If vanadium is known to get tangled in carbonaceous material and life is not required to make such materials, testing for vanadium is unlikely to more indicative of biotic origin than testing for carbon.