The search for extraterrestrial life is becoming more and more interesting as a team of scientists including Dr. Christopher Glenn of the Southwest Research Institute discover new evidence of a building block for life in the subterranean ocean of Saturn’s moon Enceladus. New modeling suggests that Enceladus’ ocean must be relatively rich in dissolved phosphorous, an element essential for life.
“Enceladus is one of the main targets in humanity’s search for life in our solar system,” said Glenn, a leading expert on extraterrestrial oceanography. He is a co-author of a research paper in Proceedings of the National Academy of Sciences (PNAS) describing this research. “In the years since NASA’s Cassini spacecraft visited the Saturn system, we have been repeatedly surprised by discoveries made possible by the data collected.”
The Cassini spacecraft discovered liquid water under Enceladus’ surface and analyzed samples when plumes of ice grains and water vapor erupted into space from cracks in the moon’s icy surface.
“What we’ve learned is that the shaft contains nearly all of the basic requirements for life as we know it,” Glenn said. “While the vital element phosphorous has not been directly identified, our team discovered evidence of its availability in the ocean beneath the moon’s icy crust.”
One of the most profound discoveries in planetary science over the past 25 years is that ocean worlds beneath a surface layer of ice are common in our solar system. These worlds include the icy satellites of giant planets, such as Europa, Titan and Enceladus, as well as distant objects such as Pluto. Worlds like Earth with surface oceans must lie within a narrow range of distances from their host stars to maintain temperatures that support liquid surface water. However, inland water ocean worlds can occur over a much wider range of distances, greatly increasing the number of potentially habitable worlds across the galaxy.
“The pursuit of the possibility of extraterrestrial habitation in the solar system has shifted focus, as we are now searching for the building blocks of life, including organic molecules, ammonia and sulfur-bearing compounds as well as the chemical energy needed to support life,” Glenn said. “Phosphorus represents an interesting case because previous work suggests that it may be rare in the vicinity of Enceladus, which could reduce the odds of life.”
Phosphorous in the form of phosphate is vital to all life on Earth. It is essential for creating DNA and RNA, energy-carrying molecules, cell membranes, bones and teeth in humans and animals, and even the sea-plankton microbiome.
Team members performed thermodynamic and kinetic modeling that simulates the geochemistry of phosphorous based on insights 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 in the ocean of Enceladus melt and predicted that the phosphate minerals would be extraordinarily soluble there.
“Basic geochemistry has an elegant simplicity that makes the presence of dissolved phosphorous inevitable, reaching levels close to or even higher than those found in modern seawater on Earth,” Glenn said. “What this means for astrobiologists is that we can be more confident than before that Enceladus’ ocean is habitable.”
According to Glenn, the next step is clear: “We need to go back to Enceladus to see if there is actually a habitable ocean inhabited.”