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Subglacial microbial life on Earth and beyond

Blood Falls, Antarctica, where microbes live under the ice. Iron and other elements under the ice oxidize when they interact with air, producing a rusty red color. Credit: Jill McKee

The search for extraterrestrial life fascinates many and prompts big questions: Are we really alone in the universe? Is our earth unique? Is it possible that extraterrestrial life is actually far from tiny green aliens and much closer to the microbial life we ​​share our planet with?

Single-celled organisms were the first life forms that evolved on Earth billions of years ago and have existed much longer than humans and other multicellular organisms. They are also metabolically diverse and can thrive. The environment that we humans perceive as extreme.Such as piping into the ocean floor into hot hydrothermal vents, into highly saline lakes, and even into rocks.

Europa – An icy moon of Jupiter

The first place to look for life beyond Earth is within our solar system, where the distances between us and potentially habitable worlds are still manageable for spacecraft flybys and even sampling missions. Venus, Mars, and many of the moons of Jupiter and Saturn are of interest to astronomers, although Europa, one of Jupiter’s 95 moons, is a particularly promising world. Europa is an icy ocean world where water bubbles up from the ocean beneath a thick layer of ice.

Although the surface temperature remains consistently below a frigid -220°F, Europa excites many astronomers as a potential site for life in our solar system because of its sub-icy ocean. As we know, water is essential for the habitability of the planet in terms of life. A polar solvent like water is essential for the biochemical reactions that drive all life on Earth and can also provide a thermally stable habitat for organisms to live and evolve.

Along with water, carbon is another important building block for life as we know it. All of life’s essential macromolecules are carbon-based—sugars, proteins, DNA, and lipids are all composed of carbon atoms arranged in various forms, including rings, sheets, and chains.

In September 2023, two independent teams of scientists found that solid carbon dioxide (CO2) probably at the level of Europa It originates from sub-glacial seas.as its location on the surface is favorable. which indicates the transport of material from beneath the ice.

One team also hypothesized that the oceans are oxidized, a chemical state that supports Earth’s current biosphere and thus favors life as we know it. Although scientists were not able to pinpoint the source of the CO.2 On Europa, the confirmation of the presence of carbon on Europa has fueled the fire of astronomers who believe it could host microbial life.

Signs of life such as organic carbon and water are said to be widespread. Bio signature, chemical or physical markers that specifically require biological origin. Although no single biosignature is sufficient to suggest life on a distant world, finding many complementary biosignatures on bodies like Europa could strengthen the argument that life, in one form or another, is present on Earth. can exist outside of

Subglacial microbial life on Earth and beyond

An illustration of NASA’s Europa Clipper spacecraft set to launch in October 2024. Credit: NASA/Wikimedia Commons

From Europa to Antarctica—a study of subglacial microbes

As a microbiological fieldwork site, Europa is about as inaccessible as it gets—it’s more than 390 million miles away, and incredibly cold. How, then, can we determine that life can survive under European conditions? One idea is to study land-based analog sites. On Earth whose conditions mimic distant worlds.

Characterized by In these ecosystems, we can gain insight into how life can persist in places that are completely inhospitable to other forms of life. Studying analog sites can also give us clues about what kinds of biosignatures might be important in different environments and help inform what researchers look for in data from future Europa-bound missions. do

Jill Mikucki, Ph.D., an associate professor at the University of Tennessee, Knoxville, studies one such analog site: Blood Falls, a feature that colors the terminus of Taylor Glacier in Antarctica’s McMurdo Dry Valleys. . There, a brackish, subglacial terrestrial ecosystem leaches iron-rich brine to the surface. The iron oxidizes on contact with the air, giving the ejected saltwater a rusty red color and giving Blood Falls its ominous appearance and name.

“Working and camping in dry valleys is another world,” said Makoki. “It can be extremely calm… penetratingly so. But if the wind picks up, it can roar.”

Part of Blood Falls’ appeal as an analog comes from its unique geographic and hydrological features. “I think Blood Falls makes a great analog for studying the marine world because it’s one of the few places where liquid moves from under the ice to the surface,” McCokey explained. “Plus, it’s shiny, so it’s like a miniature sea world that’s ridiculously exuding subglacial fluids and its microbial contents.”

These features are reminiscent of European plumes erupting from under ice. “At Blood Falls, we can study what life is like under the ice, what its transportation to the surface involves, and what it’s like to survive on the surface,” McCucci said.

In 2009, McCucci and colleagues published a paper explaining how Microbes under Taylor Glacier may be cycling sulfur and using iron as a terminal electron acceptor, a role played by oxygen for many organisms on Earth’s surface.

This type of metabolism occurs under anaerobic conditions (when oxygen is limited), which can occur in some environments when photosynthetic organisms that produce O2 Absent This ecosystem is buried deep under ice and may have been isolated from the outside world for more than 1 million years.

Mikucki has been working on subglacial environments for more than two decades, but she’s still stunned by some of her and her team’s findings. For example, microbial cells grow very slowly under ice, possibly taking a year or more to divide.

“Everything still blows my mind,” she laughed. “I wonder how long this salt water has been trapped under Taylor Glacier—and how, where, under what conditions it originated. How have these microbial communities persisted during this physical and chemical journey?” Can life survive on Europa? The jury is still out, but efforts are underway to gather more data.

Future missions to Europa

In the coming decades, we will get a better look at Europa through two missions: the European Space Agency’s JUICE (Jupiter Icy Moons Explorer), and NASA’s Europa Clipper. While the JUICE mission, launched in April 2023, aims to characterize Europa and Jupiter’s two other moons, NASA’s Clipper mission (launching in October 2024) will focus on Europa.

Clapper aims to study the composition and geology of Europa, as well as measure the thickness of the ice layer and the exchange between the surface and the ocean. Both spacecraft should reach their targets in the 2030s and then begin collecting and sending back data.

The possibility that life exists beyond Earth—and that it could be very different from what we have here—is both exciting and humbling. If we never find life outside of Earth, that would mean that what happened here was extraordinarily special. If we do, it could change what we think we know about life and show us that we are not alone in the vast universe.

Reference: Subglacial microbial life on Earth and beyond (2024, February 19) Retrieved February 19, 2024, from https://phys.org/news/2024-02-subglacial-microbial-life-earth.html.

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