NASA’s crunching the numbers — and the rocks. But it looks as though its six-wheeled Perseverance rover has found the first real evidence of life on Mars.
“This is the kind of discovery you hope for — where mind-bending observations make your heart beat just a little faster,” says NASA’s Jet Propulsion Laboratory director Laurie Leshin.
Her robotic explorer has been rolling around an ancient Mars river delta since it arrived in February, 2021. It’s been scouring the fossilised four-billion-year-old shoreline for hints of ancient microbial life ever since.
Last week, it took a look at an unusual veined boulder sitting among the sand and rubble.
To the untrained eye, it looks like any other mottled rock set with a jumble of smaller stones. But it has put astrobiologists on the edge of their seats.
“The rock exhibits chemical signatures and structures that could possibly have been formed by life billions of years ago when the area being explored by the rover contained running water,” a NASA statement reads.
Now, NASA just needs to prove it.
Hunting for organic material on Mars
Perseverance was deliberately dropped into a 400m wide valley where an ancient river once fed into Jezero Crater Lake. The mud and clay would have been ideal for microbes back when Mars was warmer, wetter, and had a much thicker atmosphere than today.
This 1m by 60cm rock is what the $US2.7 billion project was all about.
Perseverance’s SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument has produced positive results.
It seems the rock, dubbed “Cheyava Falls” after a waterfall in Arizona, contains carbon-based organic material.
On Earth, its blotched and veined surface would be a dead giveaway of fossilised microbial life.
But Mars is different. And geological processes can produce very similar results.
What the veins on Mars can tell us
First, the veins.
These calcium sulphate precipitations are common in Mars’ sedimentary rocks, “though they normally represent habitable conditions,” University of Edinburgh astrobiologist Sean McMahon said.
“My own work has shown that microorganisms inhabiting sub-surface fractures can produce chemical fossils that get trapped in calcium sulphate veins.”
Microbe colonies assemble particular sets of nutrients, mostly carbon and hydrogen, along with oxygen, nitrogen and sulphur. These make up the proteins, acids and fats necessary for life as we know it.
When they die, clusters of these materials remain behind.
But it is possible for natural geological processes to produce similar concentrations.
And that, notes McMahon, may be indicated by olivine crystals. This mineral is created by volcanic activity. It may suggest the water carrying the calcium sulphate had been too hot for life.
The ‘leopard spot’ blotches tell a story
Then there are the blotches.
These “leopard spot” black-bordered, reddish-white discolourations speckled between the veins may tell another tale.
They’re rusty red because they’re patches of oxidised (rusty) iron. The black borders contain iron and phosphate.
“These spots are a big surprise,” says Queensland University of Technology astrobiologist David Flannery.
“On Earth, these types of features in rocks are often associated with the fossilised record of microbes living in the subsurface.”
They’re also what piqued McMahon’s interest.
“These reactions are often driven by subsurface-dwelling bacteria,” he writes. “As one of the few astrobiologists to have studied reduction spots on Earth — and found evidence for biological processes within them — I am personally delighted.”
Such spots haven’t been spotted on Mars before.
But they’re not quite a smoking gun.
It’s possible natural processes can produce similar outcomes — as with the calcium sulphate veins.
“On the one hand, we have our first compelling detection of organic material, distinctive colourful spots indicative of chemical reactions that microbial life could use as an energy source, and clear evidence that water — necessary for life — once passed through the rock,” says Perseverance rover project scientist Ken Farley.
“On the other hand, we have been unable to determine exactly how the rock formed and to what extent nearby rocks may have heated Cheyava Falls and contributed to these features.”
Perseverance has one trick left
Only careful analysis in laboratories back on Earth can answer the question beyond a reasonable doubt.
“We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable,” said Farley. “Scientifically, Perseverance has nothing more to give.”
Fortunately, Perseverance has one trick left up its sleeve.
It can take core samples. “Cheyava Falls” is its 22nd such example.
When full, the rover will place them in a pile for a later mission to recover. If the $US11 billion-dollar Mars Sample Return project isn’t cancelled that is.
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Dr. Sarah Adams is a scientist and science communicator who makes complex topics accessible to all. Her articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
