To understand the life that could survive beneath the surface of Martewe can refer to some of the organisms that inhabited the greatest depths and oldest on our planet.
Mars is not just the red planet: it is also It is a wet planet On August 12, American researchers reported that there is evidence of the existence of a large reserve of liquid water at great depths beneath the planet’s rocky crust.
The data comes from the ship Mars Insight Lander NASA’s Mars Survey, which recorded more than 1,300 earthquakes on Mars over four years.
A team of researchers led by Vashan Wright, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego, studied seismic waves picked up by the lander and concluded that they had passed through layers of wet rock.
Although the surface of Mars is a barren desert, Wright’s data suggest that there are considerable volumes of water locked in rocks at depths of between 11.5 and 20 km.
“If they’re right,” says Karen Lloyd, a subsurface microbiologist at the University of Southern California in Los Angeles, “this changes things dramatically.”
Water in the subsoil of Mars opens the possibility of underground life on Mars.
In recent decades, it has been revealed that there is a vast biosphere hidden deep within the Earth. Now it seems that the same could be true on Mars. Martian life, if it exists, could well be underground.
The deep biosphere
For more than 30 years, biologists have accumulated evidence that life persists in the depths of the Earth. Researchers have drilled into the seafloor and continents, finding life in buried sediments and even between layers and crystals of solid rock.
Most of these inhabitants of the dark are unicellular microorganisms, specifically bacteria and archaeaThese two huge groups are the oldest known life forms on Earth: they have existed for more than 3 billion yearslong before animals and plants.
In the past 20 years, it has also been discovered that the deep biosphere is very diverse. “There are actually many different types of organisms living underground,” he says. Cara Magnaboscoa geobiologist at ETH Zurich, Switzerland.
Bacteria are divided into large groups called phyla; only a few dozen of these groups have been formally identified, out of an estimated 1,300 that exist.Almost all of these edges are found underground”explains Magnabosco.
And it’s not like they’re evenly distributed. A 2023 meta-analysis found that most underground ecosystems were dominated by two phyla, Pseudomonadota y FirmicutesOther types of bacteria were much rarer, but among them were phyla never seen before.
Due to the total darknessthese microbes cannot obtain energy directly from sunlight, as photosynthetic organisms on the surface do. “What is really important to highlight is that They do not depend, in general terms, on the Sun“Lloyd says.
They also receive no other inputs, such as nutrients, from above. Many of these deep ecosystems are “completely disconnected from the surface,” says Magnabosco.
Instead, these ecosystems are based on the chemosynthesis Microbes get their energy from chemical reactions that take chemicals from rocks and water in their environment. For example, they can use gases like methane or hydrogen sulfide as feedstock. “There are so many chemical reactions going on underground,” Lloyd explains. “Many of us spend a lot of time trying to find new reactions that support life.”
Chemosynthetic microbes may seem strange because they are rare in the sunny surface areas where we spend our time and are confined to the depths of the sea and the solid subsurface. But they are some of the oldest types of living organisms on Earth Some hypotheses about the origin of life assume that the first life on Earth was chemosynthetic.
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Although single-celled microbes dominate the subsurface, there are also some unusual animals. A 2011 study identified nematode worms living in water at depths of 0.9-3.6 km in South African mines. The water appeared to have been there for at least 3,000 years, suggesting the nematode population could be thousands of years old.
In 2015, a follow-up study found platyhelminthes, segmented worms, rotifers and arthropods in the water contained in a fissure at a depth of 1.4 km: The water had been there for about 12,300 years.The animals fed on a thin film of microbes on the rock surface.
To us, the deep subsurface seems like an extremely difficult place to live. Compared to the surface, microbial populations are sparse, but there is also plenty of rock to live in.
“We have a very large number of cells under our feet”says Magnabosco. In fact, according to her, about 70% of all bacteria and archaea on Earth are found underground.
It is still unclear how deep the biosphere extends. Life is assumed to have an upper temperature limit, but we don’t know exactly what it is. Nothing can live on the surface of molten lava, but some microbes can withstand surprising heat: an archaea called Methanopyrus kandleri can survive and reproduce at 122°C.
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If we go far enough underground, pressure also becomes an issue. The type of rock is also important, because it affects the chemical reactions that can occur and therefore the types of chemosynthetic microbes that can live there.
“But I can’t give a figure. [de hasta en qué profundidad existe vida] “because we haven’t found it yet. We just haven’t drilled that deep,” Lloyd says. The limit could be surprisingly deep: A study of samples from a mud volcano in 2017 suggested that life could exist 10 km below the seabed.
Part of this life develops with extreme slowness“There are definitely large parts of the subsurface, mainly beneath our oceans, where nothing really happens for millions of years,” Lloyd says. With no new nutrients coming in from above, and no way to escape, microbes in these places have very little food to eat.
“That means they don’t have the energy to create new cells,” he explains. Instead, they slow down their metabolism and are almost in stasis. “It’s actually quite reasonable that a single cell can live for thousands of years or more.”
It is this type of life – dependent on chemical reactions between rocks and water, and possibly with an extremely slow metabolic rate – which could plausibly be found in water-rich rocks deep beneath the surface of Mars.
Martian microbes?
Until now There is no solid or direct evidence of the existence of life on Mars.despite decades of unmanned missions to the Red Planet. The surface is dry and cold, and no living organisms have ever appeared in the camera shot of a rover.
However, features such as canyons suggest that Mars had water on its surface billions of years ago. Some of that water was likely lost to space, but Wright’s team concluded that much of it lies beneath the planet’s surface.
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“We know that water is a prerequisite for life as we know it,” Lloyd says. So perhaps the Martian surface used to be habitable, and now it is only the subsoil.
Like the slow-moving microbes that live deep in Earth’s oceans, Martian microbes could cling to life despite nutrient shortages. “The same kind of processes that occur in our subsurface can occur on Mars,” Magnabosco says.
The most suggestive evidence of life to date is the methane columns in the Martian air, which vary with the seasons. On Earth, methane is typically produced by microorganisms, so the gas could be waste product of subsurface life. However, Lloyd urges caution. “There are many reasons unrelated to life why there could be methane plumes,” he says.
In addition, there are many other obstacles to life in the Martian subsoil. “Life doesn’t just need water”“It needs energy and a place to be, so it needs a habitat.” We don’t yet know whether the pores in Martian rock are big enough for microbes. The chemical composition of deep rocks is also crucial, as they would be the source of chemical energy.
For Magnabosco, “the biggest mystery” about life on Mars “is whether or not it arose.” Since we don’t know how the first living beings formed from inanimate material, we don’t know whether conditions on Mars were ever suitable for the emergence of life. “If life was able to develop on Mars,” he says, “it has a good chance of having survived and still being on Mars today.”
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If this deep Martian biosphere exists, how could we find it? The obvious idea is to drill into Mars, but we would have to drill 10 km or morea tall order even on Earth. Doing that on a planet that lacks breathable air or running water? “It’s much harder,” Magnabosco says.
However, it should be possible to obtain evidence. The mission Mars Sample Return planned by NASA would bring Martian rocks to Earth: these samples could contain traces of life.
“Going after methane would be very useful,” Lloyd says. At the moment, we don’t know where the gas comes from. “If we find that water cavities are associated with the methane plumes,” that would suggest there is life, he says.
Finally, if there really is moving water on Mars, we might be able to tap into it. On Earth, things like hot springs bring water from underground to the surface. “Mars has mud volcanoes,” Lloyd says. “There are places on Mars you can go where there are samples of the deep subsurface that have been exhumed and brought to the surface.”
It may be decades before we get a definitive answer. That answer could be frustrating: Mars is much less tectonically and hydrologically active than Earth, suggesting life is scarce or nonexistent. “We could be looking for life that has not been alive for a long time”dice Lloyd.
In that case, all we might find is fossil evidence, rather than living organisms. “In any case, this is life on Mars,” he says.
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