NASA’s Cassini spacecraft spectacularly crashed into ringed planet Saturn in September 2017, after two decades in space. Astronomers continue to study Cassini’s treasure trove of data, almost two years later. NASA mission featured a flyby of Saturn’s moon Enceladus, allowing it to analyse the chemical content of oceanic plumes spewing hundreds of miles up into outer space. And a second look at this data reveals Enceladus’ oceans are far more hospitable for hosting life than ever expected.
The subsurface ocean of Saturn’s moon Enceladus boasts higher than anticipated concentrations of carbon dioxide and hydrogen and a more Earth-like pH level.
These conditions could provide a “free lunch” for living microbes, said lead researcher, the University of Washington’s Lucas Fifer.
Or, conversely, it might just mean “that there is hardly anyone around to eat it”.
The new information about the composition of Enceladus’ ocean gives planetary scientists a better understanding of the ocean world’s capacity to host life.
Enceladus is a small moon, an ocean world about 310 miles (500km) across.
Its salty subsurface ocean is of interest because of the similarity in pH, salinity and temperature to Earth’s oceans.
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Plumes of water vapour and ice particles offer a tantalising glimpse into what the moon’s subsurface ocean might contain.
But Mr Fifer and colleagues found the plumes are chemically different the ocean from which they erupt at 800 miles an hour, as the eruption process itself changes their composition.
Fifer and colleagues say the plumes provide an “imperfect window” to the composition of Enceladus’s global subsurface ocean and that the plume composition and ocean composition could be much different.
That, they find, is due to the separation of gases, which preferentially allows some components of the plume to erupt while others are left behind.
This in mind, the team returned to data from the Cassini mission with a computer simulation that accounts for the effects of this “fractionation”, for a better idea of the composition of Enceladus’s inner ocean.
And they found “significant differences” between Enceladus’s plume and ocean chemistry.
Mr said Fifer said: “It’s better to find high gas concentrations than none at all.
“It seems unlikely that life would evolve to consume this chemical free lunch if the gases were not abundant in the ocean.”
Those high levels of carbon dioxide also imply a lower and more Earth-like pH level in the ocean of Enceladus than previous studies have shown, which bodes well for possible life, too, MrFifer said.
“Although there are exceptions, most life on Earth functions best living in or consuming water with near-neutral pH, so similar conditions on Enceladus could be encouraging,” he said.
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“And they make it much easier to compare this strange ocean world to an environment that is more familiar.”
There could be high concentrations of ammonium as well, which is also a potential fuel for life.
And though the high concentrations of gases might indicate a lack of living organisms to consume it all, Fifer said, that does not necessarily mean Enceladus is devoid of life.
It might mean microbes just aren’t abundant enough to consume all the available chemical energy.