We gonna peek a little bit beyond the headlines here about the potential Mars biosignatures. Why is this such a big deal for #astrobiology ?
Here is the press release:
https://www.nasa.gov/news-release/nasa-says-mars-rover-discovered-potential-biosignature-last-year/
Some of this discovery was originally presented at the Lunar and Planetary Science Conference (LPSC) last spring. More work was done and it successfully went through peer review.
the end result was a really nice OPEN ACCESS paper in Nature.
Here it is! Enjoy!
Now let's see what the big implications are....
A geological, petrographic and geochemical survey of distinctive mudstone and conglomerate outcrops of the Bright Angel formation on Mars reveals textures, chemical and mineral characteristics, and organic signatures that warrant consideration as potential biosignatures.
The authors present evidence for formation of "poppy seeds" (little dark spots) and "leopard spots" (bigger spots with an oxidation rind, and pale centers). These are found in the organic matter -rich (relative to other nearby facies) mudstones in that location.
it is a big iron story. Oxidized Iron (Fe+) makes rocks and muds red. Reduced iron (Fe2+) is pale and soluble so it can go away. Pale stuff (like the leopard spot interiors) has less Fe3+. It's reduced.
Some of you might remember the fun during #MinCup reading about vivianite. That is a blue mineral that can form around decomposing bodies (bones) as reduced iron combines with phosphate in an anoxic setting.
For some fun macabre reading, check out: https://www.atlasobscura.com/articles/vivianite-blue-human-remains
Detailed examination of these mars samples suggests that mobilized reduced iron, combined up with phosphate and made some vivianite (see bottom of p. 336 in article).
How did that happen? Not exactly clear, but a great possibility is that some organics got oxidized, and those electrons went to sulfur and ultimately those went to iron Fe3+ to make mobile pale Fe2+. This kind of thing happens all the time on Earth in anoxic environments from microbial activity.
("follow the electrons" is always a good plan in chemistry, biology, and geochemistry.)
The authors did a great job showing that this redox cycle happened in the deposited muds themselves. It did not happen somewhere else and got carried in.
So for #astrobiology, we just went from talking about "habitability" on Mars to actual potential biosignatures.
We now have some "Where?" "When?" and "How?" clues IF this turns out to be a valid biosignature.
The "Where?" Right here in the wet muds of Jezero crater. Right where this sample was (sorta, it looks like might have gotten shifted a bit due to rock layering angles.)
"When?" First, Mars is old. These muds maybe on the young side of 3.5 BILLION years old. This is around the time photosynthesis started on Earth maybe. Old.
"How?" Probably oxidation of organics, then maybe sulfur cycling, but ultimately iron as ultimate taker of electrons.
That is a lot of clues.
So we just went beyond "hey we think we found water on Mars"...
...to here is where, when and how we think Mars MIGHT have had life metabolism cycling right here and back then.
Huge leap.
And even if it is not a life story on Mars, we will learn about Mars geochemistry.
Either way, these samples are super-exciting!
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Mike Malaska
Richard Hendricks