We may spend a lot of time pondering the possibility of microbial life on Mars, but few would argue that some of Jupiter and Saturn’s icy moons, those concealing subterranean oceans, aren’t excellent options for future discoveries in this regard.
The former’s Europa, for example, is almost certain to have a concealed hydrosphere that may even have a somewhat primitive, Earth-like chemical constituency. Plenty have wondered not just what may lurk beneath its striated crust, but how it may survive there – and a new study led by the University of Sao Paulo has put forward a possible, intriguing answer.
There’s indubitably a source of heat keeping Europa’s ocean liquid. This is very likely to be tidal heating from its interaction with Jupiter and the other Galilean moons, a source of power that also keeps Jupiter’s Io incredibly volcanic. It could also be partly due to the decay of radioactive materials, something that partly fuels our own world’s internal heat source.
As it turns out, the existence of the latter option may also have implications for life. The team of Brazilian researchers, looking for analogs of hypothetical Europa-based life on Earth, note that a bacterial species in a South Africa uses radiation to live, but not in the way you might think.
Candidatus Desulforudis audaxviator, a cacophonously-named microbe, can be found (among other places) several kilometers down the Mponeng Gold Mine in South Africa. Lacking any sunlight, deprived of oxygen, and living in high temperatures, it survives thanks to the presence of radioactive compounds, like uranium.
The radiation here breaks down water molecules into its constituent parts, a process known as water hydrolysis. These highly reactive molecules bounce into the surrounding rock, producing sulfate molecules. These savvy bacteria then use these to manufacture adenosine triphosphate, the very same molecule we use to store and transport chemical energy.
The Scientific Reports study notes that this doesn’t just allow the bacteria to thrive; it actually “dominates the biota” down there, and the authors explain that the mine environment “can be considered similar to those of the seabed of Europa.”
In fact, their calculations suggest that even a weakly irradiated subsurface ocean there would be enough to sustain such an organism. Forget uranium, they say – even decaying potassium might just do it.
This isn’t the first time radiation has been implicated in the origin or sustenance of life. A 2017 paper looking at our own pale blue dot surmised that uranium radiation slowly “cooked” the water on young Earth, driving the formation of organic chemistry more than any lightning strike ever did.
Back in 2008, a genomic analysis of this “single-species ecosystem” also revealed the bacteria can also fix life-sustaining carbon from extraneous organic matter, as well as from carbon monoxide and dioxide if available. It’s safe to say that it’s an incredibly hardy organism, so we shouldn’t be surprised to find its alien cousins beneath Europa or Saturn's Enceladus.
So, will we? It’s too early to tell, of course; we still need to confirm if the right ingredients are present. Still, it’s a thrilling possibility.
“I believe that radiation could have played a significant role on the origin of life on Earth, and on other planets and moons,” corresponding author Dr Douglas Galante, a researcher at the Brazilian Synchrotron Light Laboratory and participant of the NASA Astrobiology Institute, told IFLScience.
In fact, although not the sole source of energy in this respect, Galante added that the prominence of radiation “does widen our view of the habitable universe, as you can now think of planets very far from the habitable zone.”