The combination of seismic activity and water locked away at depth within Mars could be releasing sufficient hydrogen gas to support communities of microorganisms, says a team of scientists — and there’s a possibility we’ve already observed their presence.
Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 1,550 miles (2,500 km) from the surface of the planet. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene shows the entire Valles Marineris canyon system, over 1,240 miles (2,000 km) long and up to 5 miles (8 km) deep, extending form Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain from north-central canyons and run north. The three Tharsis volcanoes (dark red spots), each about 15.5 miles (25 km) high, are visible to the west. South of Valles Marineris is very ancient terrain covered by many impact craters. Image credit: NASA / JPL-Caltech.
Whilst there is increasing evidence of ancient surface water on Mars, today, much of it is believed to reside below the surface. However that might not stop it supporting life.
Deep within our own planet interactions between water and rock release hydrogen, particularly when accelerated by faulting and fracturing from earthquakes. This hydrogen is thought to provide energy for communities of hydrogenotrophic microorganisms, which metabolize it.
Dr. Sean McMahon is a geomicrobiologist at Yale University investigating whether similar seismic activity on Mars could support a present day alien subsurface biosphere.
“As we learn more about Mars it becomes more likely that present day habitable environments are limited to far down below the surface,” he says.
In his team’s latest study published in the journal Astrobiology, Dr. McMahon analyzed fluids held in fault zones on Earth to calculate the amount of hydrogen collected from a history of seismic activity.
Two types of fault zone rocks were analyzed: cataclasites with large angular clasts, and glassy fine grained pseudotachylites from massive impact craters. These were compared against control samples in the same geological strata but located further away from any faults.
All fault rock samples showed enriched hydrogen compared to controls, with the highest values recording around 8 moles, or 16 grams of H2 per 10 cm3 of water.
“That is supersaturated,” says Dr. McMahon, “so the gas must have been present as bubbles or gas-filled inclusions.”
In fact the rock samples analyzed contained 5 or even 6 times estimates of the concentrations of hydrogen required by hydrogenotrophs here on Earth.
“It is because similar seismic regions might be found in the Martian subsurface that makes this study exciting,” says Dr. Aditya Chopra, a planetary scientist from the Australian National University who was not involved in the research.
“This opens up the possibility of pockets where Martian life could still hang-on as long as there was enough water and other nutrients.”
However levels of free hydrogen will be limited to areas of significant seismic history.
Looking across the whole planet, Dr. McMahon and his team predicts planet-wide H2 production of less than 10 tons – only sufficient to support localized pockets of microbial activity very close to recently active fault zones.
Despite these limits, there is a small possibility we could have already spotted evidence of communities supported by this mechanism within the Red Planet.
NASA’s Mars Curiosity rover has measured significant spikes in methane, which has been suggested could be linked to Martian subsurface biomass.
Dr. McMahon believes if microbial communities are living off ‘Marsquake’-derived hydrogen they could certainly be a contributing factor.
“Some of the microbes that produce methane on Earth use hydrogen as their energy source, though methane can also form without the involvement of microbes,” he says.
“A barrier to this theory could be thick Martian permafrost preventing hydrogenotroph methane emissions reaching the surface,” says Princeton University’s Professor Tullis Onstott, who hunts for tiny lifeforms deep within the Earth.
“To account for periodic methane release into the Martian atmosphere you need some near surface methanogens, and they could get their hydrogen straight from the atmosphere.”
Even if the methane emission spikes are a red herring Dr. McMahon believes his team’s work strengthens the case for future astrobiological investigation of ancient Martian fracture systems.
“Whilst drilling significantly below the surface is not yet feasible, we could find ‘fossils’ of subsurface life exposed by erosion. And there is always more to do on Earth. Our deep biosphere provides the best search for life on Mars.”
“We need to dig deeper on Earth, and on Mars, to give us the best chance of finding microbes that live off seismogenic hydrogen,” enthuses Dr. Chopra. “Dig, baby, dig!”
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S. McMahon et al. 2016. Evidence for Seismogenic Hydrogen Gas, a Potential Microbial Energy Source on Earth and Mars. Astrobiology 16 (9): 690-702; doi: 10.1089/ast.2015.1405
