The Quest for Life Deep Below Mars’ Surface
To understand the potential for life deep below Mars’ surface, we can look to some of the oldest and deepest forms of living organisms on Earth.
Evidence of Water on Mars
Mars is not just the red planet; it’s also a wet planet. On August 12, US researchers reported evidence of a vast reservoir of liquid water deep in the rocky crust of Mars. This discovery was made using data from NASA’s Mars Insight Lander, which recorded more than 1,300 Marsquakes over four years. The research, led by Vashan Wright, a geophysicist at the University of California San Diego’s Scripps Institution of Oceanography, analyzed seismic waves that passed through layers of wet rock, suggesting water is locked in rocks 11.5 to 20 km (7.1-12.4 miles) below the surface.
Martian Life Could Be Subterranean
“If they are correct,” says Karen Lloyd, a subsurface microbiologist at the University of Southern California, “I think this is a game-changer.” The presence of underground water on Mars raises the possibility of underground life. Decades of research have revealed a vast biosphere hidden deep within Earth, and the same could be true for Mars. If life exists on Mars, it might well be beneath the surface.
Earth’s Deep Biosphere
For over 30 years, biologists have gathered evidence that life thrives deep underground on Earth. Researchers have drilled into the seafloor and continental rocks, finding life in buried sediments and within solid rock layers. Most of these organisms are single-celled microorganisms, such as bacteria and archaea, the oldest known life forms on Earth, existing for over three billion years.
Diversity in the Deep
The deep biosphere is highly diverse. “There are actually quite a lot of different types of organisms living deep underground,” says Cara Magnabosco, a geobiologist at ETH Zurich. Bacteria are divided into large groups called phyla, and many of these phyla can be found underground. A 2023 study revealed that underground ecosystems are often dominated by two phyla: Pseudomonadota and Firmicutes, with other bacteria types being rarer.
Life Without Sunlight
Unlike surface life that depends on sunlight, these deep organisms rely on chemosynthesis, obtaining energy through chemical reactions with surrounding rocks and water. “The subsurface has many, many different chemical reactions,” says Lloyd. Microbes may use gases like methane or hydrogen sulfide as their energy source, making them seem alien to us, as they live in environments devoid of sunlight.
Survival in Extreme Environments
While microbes dominate Earth’s subsurface, rare animals have also been found, such as nematode worms in South African mines, living in water that may be thousands of years old. Despite the harsh conditions, the deep underground offers plenty of habitats, with about 70% of all bacteria and archaea on Earth living below the surface.
Challenges of Subsurface Life
The extent of life deep underground is not fully known, but some microbes can withstand extreme conditions, including high temperatures and pressures. The type of rock also affects the chemical reactions and types of microbes that can survive. Life could potentially exist 10 km (6.2 miles) below the seabed, suggesting deep biospheres could be more widespread than currently known.
Potential Martian Microbes
Although there is no direct evidence of life on Mars yet, the discovery of underground water provides hope. The surface of Mars is inhospitable, but underground conditions might support life. Features like canyons suggest that Mars once had flowing water, some of which may still exist underground.
Methane as a Clue
Methane plumes in the Martian atmosphere, which vary with the seasons, are a tantalizing hint. On Earth, methane is often produced by microorganisms, but it could also have non-biological origins on Mars. Further investigation is needed to understand the source of these methane emissions.
The Future of Mars Exploration
To find evidence of life on Mars, drilling deep into the planet’s surface might be necessary, though this is a significant challenge. Missions like NASA’s planned Mars Sample Return could provide valuable clues. “Chasing the methane would be really helpful,” says Lloyd. Identifying a connection between water pockets and methane plumes could suggest the presence of life.
Final Thoughts
Discovering life on Mars might take decades and could result in finding only fossil evidence, rather than living organisms. Nevertheless, any evidence of past or present life would be a monumental discovery, redefining our understanding of life’s potential in the universe.
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