Why there are no fish on Saturn’s moon Enceladus

The solar system is full of desert worlds, ice worlds, gaseous worlds and forbidding hunks of rock, but lately it’s been looking a bit wetter and potentially more congenial to life beyond our own water world. The Cassini spacecraft, which has been exploring the Saturn system for a decade, has provided data suggesting that there’s a Lake Superior-size sea below the icy crust of Saturn’s moon Enceladus.

Cassini had already seen plumes of water vapor coming from the south pole of the moon. New data suggest that there’s a reservoir of liquid water underneath roughly 20 miles or so of ice and on top of a rocky core.

Which raises obvious questions: Is there life in that cold, dark sea? Maybe even something as frisky as a fish?

You wouldn’t want to bet the ranch, or even your aquarium, that there’s any complex life-form there. Microbes are conceivable, though. Scientists offer a range of opinions about that possibility, while acknowledging that no one really knows anything about life beyond Earth. There are no known examples — “no data,” in the words of the late scientist Stephen Jay Gould.

A quick roundup of reactions to the life-on-Enceladus question:

Luciano Iess, a professor of aerospace engineering at the University of Sapienza in Rome and the lead author of the new paper in Science that described the Enceladus sea, is not boosterish.

“Certainly to go from liquid water in contact with rock to life is a huge step,” he said. “I really think there is no life on Enceladus.” But he added, “It’s impossible to exclude it. Even if it’s very unlikely.”

Mary Voytek, NASA’s senior scientist for astrobiology, said she doesn’t know if there’s life there, “but I certainly hope so.” She added, taking the broader view, “My personal opinion is there’s water and organics pretty much everywhere. The possibility for habitable environments to have arisen is strong throughout the universe.”

Carol Cleland, a University of Colorado professor of philosophy, said, “I think life formed so quickly on Earth that it’s just not something that’s rare. What’s interesting and what’s probably rare is multi-cellular organisms.”

Jack Szostak, a professor of chemistry and chemical biology at Harvard (and a Nobel laureate), said of the Enceladus sea, “I’m sure there could be some interesting chemistry, but I think making the kind of high-energy­ carbon-nitrogen compounds that are probably needed, that seems difficult to me. . . . I think you need more energy.”

Chris McKay, a NASA astrobiologist, believes that Enceladus has the key elements needed for life: water, energy, carbon and nitrogen. He said we shouldn’t focus on the origin-of-life issue, and paraphrased the philosopher Wittgenstein. “That of which we know nothing we should pass over in silence. The origin of life we know nothing about. . . . I tend to focus on what’s required for life to survive and grow. I don’t know what’s required for life to start.”

Andrew Knoll, a professor of natural history at Harvard: “I would be very surprised if there were fish in Enceladus.” He said you need water, energy, carbon, nitrogen, phosphorous, sulfur, iron, etc., for life as we know it.

But couldn’t life on Enceladus be weird life — totally alien and bizarre?

He answered, “Games without rules have many possible outcomes.”

We don’t know how long the Enceladus sea has existed, but we do know that time is essential for the evolution of complex life. Life began very early on Earth, which has remained a habitable, and inhabited, planet for upward of 3.5 billion years. But the Cambrian explosion, when multi-cellular life appeared, was about 540 million years ago.

This leads one to assume, as Cleland does, that life is common but fish are rare. If you want to build a trilobite, or even a sea anemone or a jellyfish, much less an octopus or a dolphin or a blue whale, you need a lot of time.

Sure, the rules could be different out there in space. But remember what Gould said.

This was adapted from The Post’s Achenblog.

Joel Achenbach writes on science and politics for the Post's national desk and on the "Achenblog."
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