The hunt for extraterrestrial life has recently become more intriguing as a group of researchers, led by Dr. Christopher Glein of the Southwest Research Institute, have found new proof of a crucial component of life in the subsurface ocean of Saturn’s moon Enceladus. A vital component of life, dissolved phosphorus, should be present in relatively high concentrations in Enceladus’ ocean, according to new modelling.
“Enceladus is one of the prime targets in humanity’s search for life in our solar system. In the years since NASA’s Cassini spacecraft visited the Saturn system, we have been repeatedly blown away by the discoveries made possible by the collected data,”
said Glein, an expert in extraterrestrial oceanography.
Water On Enceladus
Phosphorus in the form of orthophosphate (e.g., HPO42-) is likely abundant in the subsurface ocean of Saturn’s moon Enceladus.
Credit: Southwest Research Institute
As ice-grain and water-vapor plumes erupted into space from fissures in Enceladus’ icy surface, the Cassini spacecraft discovered the moon’s subsurface liquid water and collected samples.
“What we have learned is that the plume contains almost all the basic requirements of life as we know it. While the bioessential element phosphorus has yet to be identified directly, our team discovered evidence for its availability in the ocean beneath the moon’s icy crust,”
Glein said.
The fact that worlds with oceans beneath a surface layer of ice are common in our solar system was one of the most important discoveries in planetary science over the past 25 years. These worlds include more distant objects like Pluto as well as the icy satellites of the giant planets, such as Europa, Titan, and Enceladus.
Searching For Life’s Building Blocks
To sustain temperatures that support surface liquid water, worlds with surface oceans like Earth must stay within a specific range of distances from their host stars. The number of habitable worlds that are likely to exist across the galaxy is greatly increased by the fact that interior water ocean worlds can occur over a much wider range of distances.
“The quest for extraterrestrial habitability in the solar system has shifted focus, as we now look for the building blocks for life, including organic molecules, ammonia, sulfur-bearing compounds as well as the chemical energy needed to support life. Phosphorus presents an interesting case because previous work suggested that it might be scarce in the ocean of Enceladus, which would dim the prospects for life,”
Glein explained.
All life on Earth depends on phosphates, which are composed of phosphorus. For the production of DNA and RNA, energy-carrying molecules, cell membranes, bones, and teeth in both humans and animals, as well as the plankton microbiome in the ocean, phosphorus is crucial.
An Elegant Simplicity
Based on knowledge gained from Cassini about the ocean-seafloor system on Enceladus, team members carried out thermodynamic and kinetic modelling that simulates the geochemistry of phosphorus. They created the most thorough geochemical model of seafloor mineral dissolution into Enceladus’ ocean during their investigation, and they made the prediction that phosphate minerals would be 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. “What this means for astrobiology is that we can be more confident than before that the ocean of Enceladus is habitable.”
The next steps are clear, Gein concludes. We must return to Enceladus to see if a habitable ocean is actually inhabited.
Reference: Jihua Hao, Christopher R. Glein, Fang Huang, Robert M. Hazen. Abundant phosphorus expected for possible life in Enceladus’s ocean. Proceedings of the National Academy of Sciences, September 19, 2022, 119 (39) e2201388119