Life on Earth can be found in the strangest of places, from tens of thousands of metres in the sea to a bubbling tar pit in Trinidad.
But scientists have suggested that life – alien life – could be swimming inside the underground oceans of a small, icy moon of Saturn.
Once seen as nothing more than a big, boring ball of ice, Enceladus (pronounced en-SELL-a-dus) is now widely seen as a top contender for hosting extraterrestrial life.
The moon, only 300 miles wide, has a liquid ocean with a rocky floor under its bright, white surface.
Scientists from Oxford University have discovered that the moon is far warmer than thought, adding to the intrigue that life is wriggling on it.
For years, heat loss was only detected by Nasa’s Cassini spacecraft on the south pole, where plumes of vapour and ice crystals shot out of cracks.
Researchers have now found similar results in the long-thought sleepy north pole, a study published in the journal Science Advances found.
The surface at the north pole was around 7°C warmer than anticipated, a difference that could only be explained by heat leaking from the ocean.
They discovered this by comparing how much energy the moon loses from its ‘warm’ (0°C) ocean as heat rises to its frigid surface (–223°C).
This cranked up the overall heat loss of Enceladus to about 54 gigawatts, the equivalent of more than 100million solar panels, showing that it’s neither heating up nor cooling down.
Why is Enceladus such a good candidate for life?
When it comes to the truth being out there, it’s all about ‘location, location, location’, explains Dr Carly Howett, the study’s co-author.
‘Enceladus is located close enough to Saturn that this massive planet can squeeze and relax its rocky core as Enceladus moves closer and further from Saturn on its elliptical orbit,’ the associate professor of space instrumentation says.
‘However, it’s not so close to Saturn that it gets pulled in and annihilated! So that gives it the energy it needs, which is the first important requirement for life.’
Heat is one of the three main ingredients for life, and Enceladus already has the other two – liquid water and the right chemicals.
But for life to thrive, the subsurface ocean of the moon need to be balanced between how much heat they lose and gain.
This balance is struck by the tidal forces of Saturn shake the insides of Enceladus, generating enough hot friction that ice melts.
Again, says Dr Howett, this all comes down to the moon being just the right distance from the sun – around 900million miles.
‘So as water bombarded the early Enceladus from comets and ice-coated dust grains, it stuck to the surface and made Enceladus water-rich,’ she explains.
‘It also got CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur) through its formation process too.
‘If our understanding of life’s chemical requirements can be extended to life, then these chemical building blocks are needed to make proteins and DNA.’
Dr Howett and her team’s findings only add to the decades of curiosity about what lies beneath Enceladus’ seas.
‘It’s not a single piece of work that has made this conclusion, but rather a body of work that increasingly points in that direction that this work adds to – a bit like clicking another piece of the jigsaw into place!’ she says.
The next step is to determine how old Enceladus’ salty seas are to see if it’s been around long enough for life to form. The Cassini mission, the results of which Dr Howett sifted through for the paper, ended in 2017.
Dr Howett says they could do this by looking at the size of silica nanoparticles – specks that make up sand – in the ice crystal plumes.
Until then, all experts like Dr Howett can do is imagine that kind of alien life that could be bopping around Enceladus’ ocean world.
‘I love the idea of space shrimp,’ she says, pointing to the Earth-dwelling kind that hang out near hydrothermal vents.
‘Something more intelligent (sorry, shrimp!), more akin to a whale would be awesome, but to be honest, anything that wiggles is good with me.’
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