Mars’ subsurface holds the right conditions for microbial life

A new study conducted by Brown University researchers suggests that Mars’ subsurface has the right conditions for present-day microbial life.

As NASA’s Perseverance rover searches for potential ancient life on the Martian surface, a new study has revealed that Mars’ subsurface may host present-day microbial life.

The study, published in Astrobiology, investigated the chemical composition of Martian meteorites – which are rocks blasted off the Martian surface and have ended up on Earth.

The research revealed that when in continuous contact with water, the rocks would generate the chemical energy necessary to sustain microbial life like that which can survive in the unlit depths of the Earth.

As these meteorites could be typical of vast swaths of the Martian crust, the researchers’ findings indicate that much of the Mars subsurface could be habitable.

“The big implication here for subsurface exploration science is that wherever you have groundwater on Mars, there’s a good chance that you have enough chemical energy to support subsurface microbial life,” explained Jesse Tarnas, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory who led the study. “We don’t know whether life ever got started beneath the surface of Mars, but if it did, we think there would be ample energy there to sustain it right up to today.”

In recent years, researchers have determined that the Earth’s depths house a substantial biome, mostly existing separately from life above the surface. Deficient of sunlight, this life survives using the by-products of chemical reactions produced when rocks encounter water.

One reaction that occurs is radiolysis, which arises when radioactive elements within rocks react with water trapped in pore and fracture space. This then breaks down water molecules into hydrogen and oxygen. The hydrogen then dissolves in the remaining groundwater, while other minerals – such as pyrite – absorb oxygen to form sulphate minerals. Microbes can ingest the dissolved hydrogen as fuel and use the oxygen preserved in the sulphates to “burn” that fuel.

These “sulphate-reducing” microbes are present more than a mile underground, in water that has been devoid of sunlight for more than a billion years.

In this new study, the research team investigated whether the conditions for radiolysis-driven habitats could exist on Mars.

The researchers discovered that in various types of Martian meteorites, all the conditions are present in sufficient abundance to support Earth-like habitats. This was particularly true for regolith breccias – meteorites sourced from crustal rocks more than 3.6 billion years old – which were revealed to have the highest potential for life support.

Unlike Earth, Mars lacks a plate tectonics system that constantly recycles crustal rocks; therefore, these ancient terrains remain largely undisturbed.

The team believe that their findings help make a case for an exploration programme that searches for signs of present-day life on Mars’ subsurface. Previous research has indicated that an active groundwater system has existed on Mars in the past, and this too could exist today.

The new research suggests that wherever there is groundwater, there is energy present to sustain life.

Brown University professor Jack Mustard, who co-led the research, added: “The subsurface is one of the frontiers in Mars exploration.”

“We have investigated the atmosphere, mapped the surface with different wavelengths of light, and landed on the surface in half-a-dozen places, and that work continues to tell us so much about the planet’s past. But if we want to think about the possibility of present-day life, the subsurface is absolutely going to be where the action is.”

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