Moon from ISS.
Credit NASA/Jeff Williams

 

The absence of surface water doesn’t preclude the potential for life elsewhere on a rocky object, like deep in the subsurface biosphere – be it at Mars or Earth’s Moon.

New research analyzes the “thickness” of subsurface regions on those worlds, places where water and life might exist in principle and whether the high pressures within those areas could rule out life altogether.

In terms of searching for life subsurface on the Moon and Mars, however, the researchers note it won’t be easy, requiring search criteria and machinery not yet in use on either neighboring locales.

The research is published in The Astrophysical Journal Letters, led by scientists at the Center for Astrophysics (CfA) at Harvard & Smithsonian and the Florida Institute of Technology (FIT).

Digging in…on Mars.
Credit: NASA Langley Advanced Concepts Lab/Analytical Mechanics Associates

Search ahead

Manasvi Lingam, assistant professor of astrobiology at FIT and CfA astronomer, and lead author of the work, explains:

“We examined whether conditions amenable to life could exist deep underneath the surface of rocky objects like the Moon or Mars at some point in their histories and how scientists might go about searching for traces of past subsurface life on these objects.”

The search ahead, while technically challenging, is not impossible, Lingam added in a Harvard-Smithsonian Center for Astrophysics statement.

Mars Express radar images of reflective regions that suggest the presence of liquid water.
Credit: European Space Agency

“Surface water requires an atmosphere to maintain a finite pressure, without which liquid water cannot exist,” Lingam stated.

“However, when one moves to deeper regions, the upper layers exert pressure and thus permit the existence of liquid water in principle,” said Lingam. “For instance, Mars does not currently have any longstanding bodies of water on its surface, but it is known to have subsurface lakes.”

Warmer, pressurized regions

Research co-author, Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard and CfA astronomer, said: “Both the Moon and Mars lack an atmosphere that would allow liquid water to exist on their surfaces, but the warmer and pressurized regions under the surface could allow the chemistry of life in liquid water.”

One can imagine robots and heavy machinery, Loeb said, that will drill deep under the lunar surface in search of life, “just as we do in searching for oil on Earth.”

But what’s the limit on the amount of biological material that might exist in deep subsurface environments?

The answer, although small, is surprising.

“We found that the biological material limit might be a few percent that of Earth’s subsurface biosphere, and a thousand times smaller than Earth’s global biomass,” said Loeb.

Moon base design. Can an assignment for future explorers be looking for lunar life?
Credit: ESA/P. Carril

Extremophilic organisms

Loeb noted that “cryophiles” — organisms that thrive in extremely cold environments — could not only potentially survive, but also multiply, on seemingly lifeless rocky bodies.

“Extremophilic organisms are capable of growth and reproduction at low subzero temperatures. They are found in places that are permanently cold on Earth, such as the polar regions and the deep sea, and might also exist on the Moon or Mars,” Loeb said.

There are many criteria involved in determining the most optimal locations to hunt for signs of life on the Moon and Mars.

“Some that we have taken into account for subsurface searches include drilling near to the equator where the subsurface biosphere is situated closer to the surface, and seeking geological hotspots with higher temperatures,” FIT’s Lingam said.

In their paper, Lingam and Loeb suggest: “The Moon was habitable shortly after its formation and it is not altogether inconceivable that some traces and markers of life might survive to this day.”

Because deep biospheres are situated underneath the surface, the researchers conclude, “detecting unambiguous signatures of biological activity is not readily feasible via remote sensing techniques. The most obvious solution is to carry out in situ studies of rocky objects in our backyard such as the Moon and Mars.”

To review the paper — Potential for Liquid Water Biochemistry Deep under the Surfaces of the Moon, Mars, and beyond – go to:

https://arxiv.org/abs/2008.08709

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