Conditions for life in the Enceladus ocean increasingly certain
Saturn’s moon plays a special role in my books. Therefore, I am always very happy when there is news about possible life in the moon’s ice ocean. Like the following. A team of scientists has apparently discovered new evidence for an important building block for life in the subsurface ocean of Saturn’s moon Enceladus. Their model calculations suggest that Enceladus’ ocean should be relatively rich in dissolved phosphorus, an essential ingredient for life.
“Enceladus is one of the most important targets in humanity’s search for life in our solar system,” said Dr. Christopher Glein of Southwest Research Institute, a leading expert in extraterrestrial oceanography. “In the years since NASA’s Cassini spacecraft visited the Saturn system, we’ve been blown away by the discoveries made possible by the data it has collected.” Among other things, Cassini detected liquid water beneath the surface of Enceladus and analyzed samples streaming into space from cracks in the moon’s icy surface that contained ice grains and water vapor – the plume of ice geysers. “We learned from this that the plume contains almost all the basic requirements for life as we know it,” Glein says. “While the element phosphorus, which is essential for life, has not yet been directly identified, our team found evidence that it is present in the ocean beneath the moon’s ice crust.”
One of the most fundamental discoveries in planetary science over the past 25 years is that worlds with oceans beneath a surface layer of ice often exist in our solar system. These worlds include the icy satellites of giant planets like Europa, Titan and Enceladus, as well as more distant bodies like Pluto. Worlds such as Earth with surface oceans must be within a narrow range of distance from their host stars to maintain the temperatures that allow liquid water to exist at the surface. However, worlds with water oceans in their interiors can occur at a much larger range of distances, greatly increasing the number of habitable worlds in the galaxy.
“The search for extraterrestrial habitability in the solar system has shifted as we now look for the building blocks for life, including organic molecules, ammonia, sulfur-containing compounds, as well as the chemical energy needed to sustain life,” Glein said. “Phosphorus is an interesting case because previous work has suggested it may be in short supply in Enceladus’ ocean, which would dim the prospects for life.”
Phosphorus, in the form of phosphates, is vital to all life on Earth. It is essential for the formation of DNA and RNA, energy-bearing molecules, cell membranes, bones and teeth in humans and animals, and even the microbiome of plankton in the ocean.
The team members performed thermodynamic and kinetic modeling simulating the geochemistry of phosphorus based on what they learned from Cassini about the ocean floor system on Enceladus. In the course of their research, they developed the most detailed geochemical model to date of how seafloor minerals dissolve in Enceladus’ ocean and predicted that phosphate minerals are unusually soluble there.
“The underlying geochemistry has an elegant simplicity that makes the presence of dissolved phosphorus inevitable, reaching levels close to or even higher than those in modern Earth seawater,” Glein said. “For astrobiology, this means we can assume with greater certainty than before that Enceladus’ ocean is habitable.”
The next step, according to Glein, is clear: “We need to go back to Enceladus to see if a habitable ocean is actually inhabited.”