We may learn more about the secrets of Martian life deep in a mine near Timmins, Ontario.
Researchers have sampled Kidd Mine’s groundwater and creek for decades to better understand the microbial life that thrives there by using energetics in the fluid — derived from reactions with the rocks — that drives their metabolism. What’s more, the groundwater has been largely isolated from the surface for more than a billion years, which is roughly around the period when multicellular life began on Earth.
“That [analogue] is important because if you think about the biosphere on the surface of Earth, it’s a whole lot of organic carbon getting cycled around, and most of that organic carbon was created by photosynthetic organisms,” said Jesse Tarnas, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in California who led a new study while completing his PhD at Brown University.
The research could shed light on how Martian microbes survive in a sheltered zone away from the radiation-laden desert surface, which is dominated by a low-pressure carbon dioxide atmosphere. All of these factors make it difficult to think of even hardy life as we know it surviving there today. The Kidd Mine could therefore be a keystone in informing our research on the Red Planet.
“If there is groundwater underground on Mars, which is still definitely an unknown, then there isn’t a habitable surface environment for organic carbon to be leached down from into the groundwater,” Tarnas said. “So all of the energy produced there [on Mars] would need to just come from the water rock reactions, as it does in Kidd Creek.”
The research was published in the journal Astrobiology and includes Brown University professor Jack Mustard (who supervised Tarnas) and Professor Barbara Sherwood Lollar of the University of Toronto (who regularly performs groundwater research with a team at Kidd Creek.)
The research could help the newly-landed NASA Perseverance rover as it begins venturing further from its landing zone in Jezero Crater. Perseverance is a surface-focused rover looking to find potential rocks that may have promise for ancient life, then to cache those for a future sample-return mission to bring back to Earth in a few years. Just outside the crater, however, orbital pictures have spotted a delta and a region of megabreccias — huge rocks cemented together with finer material — that could yield sediment or rocks that used to be underground.
“These huge blocks of megabreccia … came from a meteorite impact having broken up all that rock. [The impact] placed it on the surface, and erosion over time exposed these nice cross-sections,” Tarnas said.
Such samples could show potential exposure to groundwater and, through their composition, could help researchers gain insight into what kind of redox energy production would be generated millions or billions of years ago, depending on how recently the rocks were blown out of underground. (Redox reactions involve transferring electrons between chemical species, with more common examples on Earth including metal corrosion and burning fuel.)
Tarnas’ new study continues from research published in 2018 discussing how water-rock reactions may produce hydrogen-reducing compounds in ancient Martian rocks, as well as where groundwater may be thermodynamically stable enough for microbes billions of years ago.
In the new study, he said, his team was considering whether there would be sufficient chemical energy on Mars to sustain subsurface microorganisms, and that’s where Kidd Creek came in perfectly.
“It is dominated by sulphate reducers, and sulphate reducers are nearly ubiquitous in the deep subsurface in places that we access to great depths,” Tarnas said. “They’re the predominant biomass in that whole microbial community. It’s pretty well understood, on Earth, how [they use] hydrogen and methane as a reductant and sulphate as an oxidant.”
The rocks have a low abundance of radionucleides, or a species of atoms that emit radiation while naturally decaying. That said, the decay will break apart neutral water molecules over time into water’s constituent oxidants and reductants — and there’s plenty of water available in Kidd Creek. Hydrogen, one of the reductants, can be directly used by microbes, Tarnas said. Yet a lot of the oxidants, like hydrogen peroxide, are harder to use; instead, the microbes will prefer sulphur that hydrogen peroxide will oxidize from minerals in nearby rocks.
“That’s a way of kind of sustaining … microbial communities in fluids that are more than a billion years old,” Tarnas said. “On Mars, we were interested in seeing if we could constrain the amount of energy that was produced with the same process of radiology. We had to start figuring out how to do that, because we can’t just go to Mars, grab whatever rocks we like and analyze them in the lab.”
Their solution was to turn to Martian meteorites that have fallen on Earth and to get a good variety of samples from what is available. “They [the meteorites] told us all the different parameters all the different variables that needed to be constrained, for us to make the calculation of redox energy available in the subsurface,” Tarnas said.
One of the next big steps, he added, is to look for groundwater on Mars itself. NASA’s InSight lander can probe under the surface, and orbital radar is available from a few satellites; that said, although the instrumentation on these missions can look at the subsurface, they are not quite optimized for groundwater. That will require a brand-new mission concept when the scientific community (and the associated funding) is ready to produce it.
This biweekly column by Canadian science and space journalist Elizabeth Howell focuses on a trending news topic in Canadian astronomy and space.
