Scientists have detected the presence of the sixth and final essential ingredient of life in ice grains spewed into space from the ocean of Saturn’s moon Enceladus.
Previous studies had spotted signs of the other five elements needed for life—carbon, hydrogen, nitrogen, oxygen and sulfur—in material from Enceladus’s ocean, according to the Atlantic’s Marina Koren. Now, in a paper published Wednesday in the journal Nature, researchers have added phosphorus to that list. The presence of this element is thought to be the “strictest requirement of habitability,” the authors write in the paper.
“This was basically the last piece that was needed to finally, now, deem Enceladus’s ocean to be habitable without any doubt,” Frank Postberg, a co-author of the study and a planetary scientist at the Free University of Berlin, tells Vice’s Becky Ferreira.
The finding makes Enceladus “the most promising place, the lowest-hanging fruit, in our solar system to search for extraterrestrial life,” Carolyn Porco, a planetary scientist who was not involved in the research, tells National Geographic’s Charles Q. Choi.
Phosphorus is an integral part of life on Earth. It’s the second most abundant mineral in the human body, behind calcium, and it’s key to forming bones, teeth, cell membranes and DNA. The element is a part of some 550 different minerals on Earth and is the 12th most abundant element in the planet’s crust.
But until now, astronomers had never identified phosphorus in the ocean of another world, according to the new paper. Of the six elements essential for life, it “is by far the least common in the universe,” Postberg tells National Geographic.
Scientists made the new discovery thanks to data from the spacecraft Cassini, which spent 13 years exploring Saturn and its moons. Its mission ended with a dive into Saturn’s atmosphere in 2017.
As Cassini collected information, Enceladus quickly emerged as a fascinating candidate for study. The moon is covered by an icy crust, with its global ocean sandwiched between that outer layer and its rocky core. Eruptions on Enceladus shoot plumes of ice grains and gas through cracks in its crust into space. These ejected materials form Saturn’s E ring, so Cassini could learn about what’s inside the massive ocean by studying that ring.
The researchers examined Cassini’s data on 345 ice grains from the E ring, and they detected the presence of phosphates—chemical compounds containing phosphorus—in nine of them. They found that phosphorus concentrations may be 100 times higher in Enceladus’s ocean than in Earth’s oceans, per Vice.
Manasvi Lingam, a physicist at the Florida Institute of Technology, published a 2018 paper that argued based on modeling that oceans like Enceladus’s would have less phosphorus than Earth’s. Lingam, who was not involved in the new study, tells Space.com’s Sharmila Kuthunur that the discovery “overturns the findings from my past model.”
Still, the team was not sure how Enceladus had gotten such high amounts of phosphates in the first place. So, they performed some lab experiments that suggested the moon’s ocean hosts lots of dissolved carbonates, just like soda. In this way, the so-called soda ocean can dissolve phosphate-filled rocks, leading to the high concentrations of phosphates in the water, per the New York Times’ Katrina Miller.
“No one would be surprised if there’s phosphate in the rock of Enceladus. There’s phosphates on comets … it is not a big deal,” Postberg tells Space.com. “The big deal is that it is dissolved in the ocean, and with that, [it’s] readily available for the potential formation of life.”
The findings also suggest that oceans on similar worlds, like Jupiter’s moon Europa, could also contain phosphorus, writes National Geographic. The question now is whether this habitable ocean actually contains any life.
“We don’t know yet if this very habitable place is actually inhabited,” Postberg tells the New York Times. “But it is certainly worth looking.”