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Abundance of gases in Enceladus’s ocean are a potential fuel, if life is there to consume it

There is hardly anyone around to eat it.

Enceladus is a small ocean world covered in ice — one of more than 60 confirmed moons orbiting Saturn. It’s 25 times smaller than Earth and almost ten times as far from the sun, yet in recent years, it’s given scientists many reasons to think it should be the next target in our search for worlds where extraterrestrial life could exist.

Now, new research has suggested that the concentration of carbon dioxide and hydrogen on the subsurface ocean of Saturn’s moon is probably higher than previously thought. Moreover, it has a more Earthlike pH level, suggesting it has conditions favorable to life.

Lead researcher Lucas Fifer, a UW doctoral student in Earth and space sciences said, “The presence of such high concentrations could provide fuel — a sort of chemical “free lunch” — for living microbes. Alternatively, it could 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.”

Cassini spacecraft detected the emission of plumes of water vapor and ice particles- many miles into space from the sea through cracks in Enceladus‘ ice-encased surface give a fascinating glimpse into what the moon’s subsurface ocean may contain.

When scientists studied it, they found that the plumes are not chemically the same as the ocean from where they emerged as the eruption process itself changes their composition.

Scientists noted, “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 plume fractionation, or the separation of gases, which preferentially allows some components of the plume to erupt while others are left behind.”

Scientists then focused on Cassini’s data that accounts for the effects of fractionation, to get a clearer idea of the composition of Enceladus’s inner ocean’s. They found “significant differences” between Enceladus’s plume and ocean chemistry.

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 Earthlike pH level in the ocean of Enceladus than previous studies have shown. This bodes well for a possible life, too.”

“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. Moreover, they make it much easier to compare this strange ocean world to a more familiar environment.”

“There could be high concentrations of ammonium as well, which is also a potential fuel for life. Also, though the high concentrations of gases might indicate a lack of living organisms to consume it all that does not necessarily mean Enceladus is devoid of life. It might mean microbes aren’t abundant enough to consume all the available chemical energy.”

In other words, he said: “Given that there’s so much free lunch available, what’s the greatest amount that life could be eating to still leave behind the amount we see? How much life would that support?”

“Thanks to Cassini, we know about Enceladus’ ocean and the types of gases, salts, and organic compounds that are present there. Studying how the plume composition changes can teach us yet more about this ocean and everything in it.”

“Future spacecraft missions will sample the plumes looking for signs of life, many of which will be affected just by the eruption process. So, understanding the difference between the ocean and the plume now will be a huge help down the road.”

Scientists will present their work June 24 at the astrobiology conference AbSciCon2019 in Bellevue.

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