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Searching for life in alien oceans may be more difficult than scientists previously thought, even when we can sample these extraterrestrial waters directly.
A new study focusing on Enceladus, a moon of Saturn that sprays its ocean water into space through cracks in its icy surface, shows that the physics of alien oceans could prevent evidence of deep-sea life from reaching places where we can detect it.
Published today (Thursday, 6 February 2025) in Communications Earth and Environment, the study shows how Enceladus’s ocean forms distinct layers that dramatically slow the movement of material from the ocean floor to the surface.
Chemical traces, microbes, and organic material — telltale signatures of life that scientists look for — could break down or transform as they travel through the ocean’s distinct layers. These biological signatures might become unrecognisable by the time they reach the surface where spacecraft can sample them, even if life thrives in the deep ocean below.
Flynn Ames, lead author at the University of Reading, said: “Imagine trying to detect life at the depths of Earth’s oceans by only sampling water from the surface. That’s the challenge we face with Enceladus, except we’re also dealing with an ocean whose physics we do not fully understand.
“We’ve found that Enceladus’ ocean should behave like oil and water in a jar, with layers that resist vertical mixing. These natural barriers could trap particles and chemical traces of life in the depths below for hundreds to hundreds of thousands of years. Previously, it was thought that these things could make their way efficiently to the ocean top within several months.
“As the search for life continues, future space missions will need to be extra careful when sampling Enceladus’s surface waters.”
Using computer models similar to those used to study Earth’s oceans, the study has important implications for the search for life in the solar system and beyond. As scientists discover more ice-covered ocean worlds orbiting the outer planets and distant stars, similar ocean dynamics could confine evidence of life and its building blocks to deeper waters, undetectable from the surface. Even on worlds like Enceladus, where ocean material is conveniently sprayed into space for sampling, the long journey from deep ocean to surface could erase crucial evidence.
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