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Saturday, 13 August 2016

Martian stromatolites?

Tabby's star has gotten weirder - the mystery star that showed behaviour so strange that some people looked to alien mega-structures as an explanation - has showed yet more strange behaviour.

But I'm not posting on that today. Why? Because Tabby's star was doing unexplained things before. The interesting bit is the explanations people will come up with... and that's going to take a while to develop. I've already posted plenty on the subject, here, here, here, and here.

Sorry, I couldn't resist putting this in again ('cause it's probably not aliens)...

All the Tabby's star fuss has reminded me of something I read last year, and never got the chance to follow up on: That the Curiosity Mars rover may (and I cannot over emphasis that 'may') have spotted signs of stromatolites .

It's well worth following that link. If you're not down with the microbial terminology: Stromatolites are stone structures built by colonies of microbes for protection, often in lake beds. The colonies build them by trapping floating dust particles and cementing them into a solid structure.

Above: Stromatolites: Odd swirly rocks made by microbes....

On Earth some stromatolites are so well made that they've survived nearly 4 billion years, and are the oldest unambiguous evidence of life on earth.  And on Mars...

Martian microbe houses:
Nora Nofke is Mrs Stromatolites - she has spent her whole career studying them - and some of the rock structures photographed by the Curiosity rover bear a striking resemblance to fossilised stromatolites, as she reported to the journal Astrobiology.

Above: Some of the rocks seen by Curiosity resemble (weathered by billions of years)  stromatolites. Image courtesy of JPL.

Nofke isn't claiming to have found definitive evidence of Martian life. Like the micro tunnels in martian rocks that I wrote about a few weeks back, this looks like something made by life, but 'looks like' ain't proof. The rise and fall of the claims of Martian microbes being found fossilised in the ALH84001 meteorite show just how cautious anyone advancing such a claim needs to be.

That said... according to someone who has spent their whole career studying stromatolites... these rocks look very like a stromatolite formation.

Nofke's peers are sceptical because that's the job of a scientist. But they agree she's done a good job with the data to hand:

“I’ve seen many papers that say ‘Look, here’s a pile of dirt on Mars, and here’s a pile of dirt on Earth,’” says Chris McKay, a planetary scientist at NASA’s Ames Research Center and an associate editor of the journal Astrobiology. “And because they look the same, the same mechanism must have made each pile on the two planets.That’s an easy argument to make, and it’s typically not very convincing. However, Noffke’s paper is the most carefully done analysis of the sort that I’ve seen, which is why it’s the first of its kind published in Astrobiology.”

The only way to get a definitive answer would be to bring samples of the possibly-stromatolites back to Earth and subject them to the full battery of analysis we have here - and that's not likely to happen any time soon. Even so, together with recent finds of organic carbon and (tiny amounts of) liquid water on modern Mars, Nofke's analysis adds fuel to speculation that Mars might have once been called home by something.

Nofke's paper from last year can be found here.
Above; Stromatolites  growing in a shallow lake on Earth. Mars once had shallow lakes like this so.... maybe...


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