Scientists have long assumed that the earliest life on Earth required a few basic prerequisites including water and an energy source — in this case, the Sun — in order to get going. With that in mind, it makes sense to look for similar conditions elsewhere in the Solar System if your goal is to find extraterrestrial life. Earth might seem special in this regard but water is actually fairly abundant in our system, and Jupiter’s icy moon Europa is quickly becoming a prime candidate in the search for life.

In a new study published in Scientific Reports, researchers focus on Europa’s potentially life-giving cocktail of liquid water and gravity-generated heat emanating from its core. The paper draws some very interesting parallels between Europa and certain places here on Earth where the recipe for life is ideal for bacteria to thrive without the presence of sunlight.

If life exists deep within Europa, sunlight would be hard to come by. The moon’s icy shell is thought to be over six miles thick, with an ocean lying beneath that stretches over 60 miles into the planet. That’s a whole lot of water, and it’s kept warm by tidal forces generated by its parent, Jupiter. If this sounds familiar, it’s likely because Saturn’s ice-covered moon Enceladus has a similar relationship with its parent planet, and is also thought to have a deep ocean just beneath its frosty crust.

To get an idea of how life could potentially thrive in the inky black depths of Europa, the researchers sought examples of microbes that live their lives without help from the Sun. They found what they were looking for in ground water samples from the Mponeng gold mine in South Africa. There, deep underground, bacteria live and die without ever seeing the sun, and it has its very own way of generating the energy it needs to survive.

“This very deep subterranean mine has water leaking through cracks that contain radioactive uranium,” Douglas Galante, co-author of the work, explains. “The uranium breaks down the water molecules to produce free radicals (H+, OH-, and others), which attack the surrounding rocks, especially pyrite (iron disulfide, FeS2), producing sulfate. The bacteria use the sulfate to synthesize ATP [adenosine triphosphate], the nucleotide responsible for energy storage in cells. This is the first time an ecosystem has been found to survive directly on the basis of nuclear energy.”

The scientists believe that this primitive form of life could be the key to understanding how life began on Earth, and also hint at what might be going on deep within Europa.

“The ocean bed on Europa appears to offer very similar conditions to those that existed on primitive Earth during its first billion years,” Galante notes. “So studying Europa today is to some extent like looking back at our own planet in the past.”

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