An icy moon in our own solar system could support life, according to new findings.
Enceladus – a tiny snowball that orbits around Saturn – might contain under its icy shell an entire ecosystem, scientists have suggested.
That’s after new findings that detected molecular hydrogen coming from the moon, meaning that it is more geologically alive than previously thought. And that detection signals that conditions to support life could exist on Enceladus.
“We know that the ingredients for life are water, organic molecules and energy,” says Caitriona Jackman, a space environment lecturer, from the University of Southampton. “We’ve seen evidence of water and chemical elements before, but we really have’t had direct evidence of the energy sources that are capable of fuelling life.”
“That’s what’s very significant here: this molecular hydrogen is a direct observation of an energetic process that is potentially capable of fuelling life.”
But more than anything the research highlights what we still need to know. The tragedy is that the Cassini spacecraft that revealed perhaps the greatest hope for life in our solar system, won’t actually be able to find out whether there’s anything there.
“Cassini is right at the end of its lifetime,” says Lewis Dartnell, an astrobiologist from the University of Westminster. “The decision has already been made to deliberately plunge Cassini into the atmosphere of Saturn.”
That’s being done to protect any potential life in the solar system. Forcing Cassini to destroy itself will terminate any potential hitchhikers that it’s picked up along the way.
“It’s about to go out with a bang,” says Professor Dartnell. “It’s almost like this was its swan song, just before its mission comes to an end.
“The frustrating thing is that we’ve discovered this and now won’t have any opportunity to follow up, to find out what Enceladus is like. But in the longer term – this has made the case even stronger now for going back to Saturn, going back to Enceladus, and exploring it much more closely.”
Anything that we or a probe did meet wouldn’t be able to shake our hands or greet us, Professor Dartnell points out. It will be a single-celled organism adapted to living in its harsh, hot and wet environment and little else.
But the kinds of things we could learn from meeting even the simplest life form would be profound, offering insights into the nature of life itself.
The first job of astrobiologists like Professor Dartnell would be to “peer under the bonnet and look into the machinery and the engine of these cells”. They’d explore whether alien life uses DNA in the same way life on earth does, and if it lives using the same kinds of biochemistry. Alien life may use the same toolkit, but to assemble something entirely different – the same Lego bricks, but to assemble something unlike anything seen by anyone on Earth.
More broadly, finding life on Enceladus would signal a profound shift in the chances that Earth isn’t just a unique accident.
“At present, we know of only one genesis of life (the one that led to us), so it is still possible that life could be an incredibly rare fluke,” writes David Rothery, professor of planetary geosciences at the Open University. “If we knew that life had started independently in two places in our solar system, then we could be pretty confident that life also got started on some of the tens of billions of planets and moons around other stars in our galaxy that also have the right conditions.”
But first we have to get there. Enceladus – which is only around the size of the UK from side to side – was a spectacular afterthought for Cassini, since nobody knew what surprises it contained, but it has made a compelling case for heading back there again.
Such a craft could be made to look specifically at Enceladus, says Ms Jackman, who has worked on the Cassini mission. If it were, “it would have all these questions in mind”.
“It would specifically look for molecular hydrogen, using a trajectory that would take it close to the moon on multiple occasions”, so that we could get a better sense of whether the amount of hydrogen varies over time.
“The more measurements we can get, the better sense we have of the variability of this source,” she says. “This paper – while a big advance – is one measurement, so we don’t really have a sense of how variable that source is.”
We might have to make a couple of trips – each taking years to plan, build and then execute – before we actually get a proper look at any life that might be there on Enceladus. But we can gradually learn more about the icy moon, using a range of techniques, including landing a probe on its surface and then drilling and melting down beneath its icy shell.
“When that time comes, we’re going to want to get a probe down into this subsurface sea – this hidden, alien sea,” says Professor Dartnell. That would be carrying with it special detection equipment that could look out for the special chemistry that forms the building blocks of life.
“We could dive down to the sea floor and find where these hot spots – hydrothermal vents, which will be the focus for our activity. Those are found in our own oceans – thing like black smokers, which serve as an oases of life in the cold dark depths of earth oceans.
“There, we find these really concentrated bubbles of activity and life. We might hope to find something similar on Enceladus.”
Enceladus itself was never meant to be a particular object of study by Cassini. But that all changed in 2005, when the first flyby indicated that there was far more to the moon than researchers had thought.
Scientists have been continually surprised by how alive the moon appeared to be, and conducted extra examination of it as well as Saturn.
“I think Cassini has more than covered its costs in terms of fantastic discoveries that it’s made,” says Ms Jackman. “Cassini was planned with a certain set of science goals. Those have been met and exceeded.”
“Enceladus is a huge treat and a huge bonus; something we didn’t expect to be anything more than another icy satellite. It turns out to be a moon that has a huge impact on the dynamics of Saturn’s environment.
“This small icy moon has been a delight to study. Discoveries like this are the icing on the cake. They’re pushing forward our understanding. I think it’s just amazing to study different processes. it’s a really tantalising result.”
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