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A key chemical building block of life has been found on Saturn's moon Enceladus.

Phosphorus was detected in salty ice grains that were released into space by plumes that erupt between the cracks of the moon's ice shell.

An ocean exists beneath the thick, icy surface of Enceladus, and plumes of material regularly release from geysers at the moon's south pole.

That material becomes incorporated into Saturn's outermost E ring.

Video above: James Webb Telescope spots icy moon spewing massive water plume

Scientists used data from NASA's Cassini mission, which studied Saturn and its moons between 2004 and 2017. The spacecraft flew through the plumes of Enceladus and Saturn's E ring many times, and Cassini's Cosmic Dust Analyzer detected minerals and organic compounds necessary for life.

Previously, researchers detected the presence of sodium, potassium, chlorine and carbonate compounds in the ice grains collected and analyzed by Cassini. Now, scientists can add phosphorus to the list. A study detailing the findings was published Wednesday in the journal Nature.

"Phosphorus in the form of phosphates is vital for all life on Earth," said lead study author Dr. Frank Postberg, a professor of planetary sciences at Freie Universität Berlin, in a statement. "It is essential for the creation of DNA and RNA, cell membranes, and ATP (the universal energy carrier in cells) for example. Life as we know it would simply not exist without phosphates."

It's the first time that phosphorus has been discovered in an ocean beyond Earth.

"Previous geochemical models were divided on the question of whether Enceladus' ocean contains significant quantities of phosphates at all," Postberg said. "These Cassini measurements leave no doubt that substantial quantities of this essential substance are present in the ocean water."

A habitable ocean on another world

The data revealed high concentrations of sodium phosphates, or molecules that chemically bind sodium, oxygen, hydrogen and phosphorus together, inside the ice grains.

The collective detection of phosphorus and other organic compounds in Enceladus' ocean suggests that it could be habitable for life, if it exists on the icy moon, the researchers said.

"By determining such high phosphate concentrations readily available in Enceladus' ocean, we have now satisfied what is generally considered one of the strictest requirements in establishing whether celestial bodies are habitable," said study coauthor Dr. Fabian Klenner, postdoctoral researcher at the University of Washington, in a statement.

Although the ocean exists beneath an ice shell, there are indications of hydrothermal environments along the seafloor that keep the ocean at a warmer temperature.

"The important part for habitability is that we found phosphates that have been dissolved in Enceladus' ocean and, with that, are readily available for the formation of potential life," Postberg said.

"In most cases, phosphates (on Earth and elsewhere in the solar system) are locked up in rocky minerals, but on Enceladus, they are dissolved in large quantities (as salts) in the ocean."

The researchers also conducted lab experiments to model Enceladus' salty ocean, and they determined the phosphate concentrations are at 100 times and possibly up to 1,000 times higher than in Earth's oceans. That's because "soda oceans," or those rich in carbonates and carbon dioxide like the one on Enceladus, can dissolve large amounts of phosphates that are otherwise locked inside rocky minerals, Postberg said.

"High phosphate concentrations are a result of interactions between carbonate-rich liquid water and rocky minerals on Enceladus' ocean floor and may also occur on a number of other ocean worlds," said study coauthor Christopher Glein, a planetary scientist and geochemist at Southwest Research Institute in San Antonio, Texas, in a statement. "This key ingredient could be abundant enough to potentially support life in Enceladus' ocean; this is a stunning discovery for astrobiology."

Some of the additional ocean world moons around Jupiter and Saturn include Europa, Titan and Ganymede. Future missions to Europa, like the European Space Agency's Jupiter Icy Moons Explorer and NASA's Europa Clipper, could determine more about the ingredients within these oceans.

Searching for signs of life

Although the Cassini mission ended by intentionally burning up in Saturn's atmosphere in 2017, the data collected by its instruments is changing the way scientists understand Enceladus and similar ocean worlds, which may be the best bet for finding life beyond Earth across our solar system.

"This latest discovery of phosphorus in Enceladus' subsurface ocean has set the stage for what the habitability potential might be for the other icy ocean worlds throughout the solar system," said Linda Spilker, planetary scientist and Voyager project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, in a statement. Spilker, who served as Cassini's project scientist, was not involved in the study.

"Now that we know so many of the ingredients for life are out there, the question becomes: Is there life beyond Earth, perhaps in our own solar system? I feel that Cassini's enduring legacy will inspire future missions that might, eventually, answer that very question," Spilker said.

Although the building blocks of life and conditions for habitability exist on Enceladus, no actual life has been detected yet.

"Having the ingredients is necessary, but they may not be sufficient for an extraterrestrial environment to host life," Glein said. "Whether life could have originated in Enceladus' ocean remains an open question."

"The next step is clear — we need to go back to Enceladus to see if the habitable ocean is actually inhabited," said study coauthor Dr. Nozair Khawaja, a planetary scientist and postdoctoral researcher at Freie Universität Berlin.

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Sending a dedicated mission to Enceladus is a priority for astronomers. Plans are underway to design the Enceladus Orbilander, which would both orbit the moon and land on the surface. If the mission were to launch later this decade, it would likely arrive at the distant moon in the early 2050s.

A spacecraft capable of landing on plume deposits on Enceladus could perform a chemical analysis to further investigate the subsurface ocean, said planetary geochemist Mikhail Zolotov, a research professor at Arizona State University and author of an accompanying News & Views article to the Nature study. Zolotov did not participate in the study.

"Those plume deposits could be taken inside a lander, melted, and analyzed for dissolved salts, gases, organic compounds, and possible biosignatures that all will characterize oceanic chemistry and habitability," Zolotov said.

Saturn's innermost moon, which resembles the Death Star from Star Wars, may be a "stealth" ocean world, according to new research.

Mimas, which is the smallest and closest to Saturn of the ringed planet's 82 moons, may contain a liquid internal ocean.

"If Mimas has an ocean, it represents a new class of small, 'stealth' ocean worlds with surfaces that do not betray the ocean's existence," said study author Alyssa Rhoden, a scientist Southwest Research Institute in Boulder, Colorado, in a statement.

The study was published last week in the journal Icarus.

Mimas was first discovered in 1789 by English astronomer William Herschel as a tiny dot near Saturn. The Voyager probes imaged the small moon in 1980, and NASA's Cassini mission conducted flybys of it while studying Saturn between 2004 and 2017.

The moon is only 115,000 miles from Saturn and takes just over 22 hours to complete one orbit around the planet. Mimas is covered in craters, but the largest one is 80 miles across and gives the moon its distinctive Death Star appearance.

Scientists have long been intrigued by Mimas because it's likely made almost entirely of ice. Craters scattered across the moon suggest that its surface has remained frozen for a long time.

However, before the Cassini mission came to an end in 2017, it detected an oscillation in the moon's rotation that suggested Mimas may contain a subsurface ocean.

Our solar system is home to multiple ocean worlds or moons where oceans exist beneath thick ice shells, including Jupiter's moon Europa and Saturn's moons Titan and Enceladus. These differ from Earth, which is at the right distance from the sun to include liquid water oceans on its surface.

Interior water ocean worlds, or IWOWs, are much further from the sun — but they could still support life within their oceans.

"Because the surface of Mimas is heavily cratered, we thought it was just a frozen block of ice," said Rhoden, who is also the co-leader of NASA's Network for Ocean Worlds Research Coordination Network.

"IWOWs, such as Enceladus and Europa, tend to be fractured and show other signs of geologic activity. Turns out, Mimas' surface was tricking us, and our new understanding has greatly expanded the definition of a potentially habitable world in our solar system and beyond."

Mimas is tidally locked in its orbit around Saturn, meaning that the same side of the moon always faces the planet — like our moon as it orbits Earth. The researchers believe a phenomenon called tidal heating allows for the subsurface ocean to exist on Mimas.

Tidal heating causes an internal increase of temperature in a moon due to its gravitational relationship with a planet.

To re-create the oscillation detected in Mimas' rotation by Cassini, the researchers used models to show that tidal heating occurring in the small moon is enough to maintain an ocean beneath an ice shell that is between 14 to 20 miles thick.

This finding could be useful as future spacecraft study ocean worlds in our solar system, but it also shows that Mimas and Saturn's other moons may be worth observing more moving forward. Future spacecraft could confirm that Mimas is indeed one of these interior water ocean worlds.

"Evaluating Mimas' status as an ocean moon would benchmark models of its formation and evolution," Rhoden said.

"This would help us better understand Saturn's rings and mid-sized moons as well as the prevalence of potentially habitable ocean moons, particularly at Uranus. Mimas is a compelling target for continued investigation."

Above video: Closest alignment of Jupiter, Saturn in nearly 800 yearsRight before Christmas, the two largest planets in our solar system formed a "double planet," an incredible spectacle that hasn't happened in more than 800 years. Well, soon one more planet will be joining them for another rare celestial sight. This weekend, Jupiter, Saturn, and Mercury will form a triangle for the first time since 2015, according to EarthSky.Dubbed a "planetary trio" or a "triple conjunction," the three planets will appear close together just after sunset from Jan. 8 through Jan. 11. Tonight, Mercury will start to move closer to Saturn, which will appear below Jupiter. So when's the best date to see the triple conjunction? The tightest grouping of these planets will occur on Sunday. The best way to catch the planetary trio is find a spot with an unobstructed view of the horizon, and look toward the direction of the sunset. It's important to start searching for the planets no later than 45 minutes after the sun sets because they will fall out of view beneath the horizon by nightfall, according to EarthSky. It might be difficult to spot the planets (especially Saturn, the dimmest of the three planets) while they're competing with the glow of the sunset. So it's a good idea to bring along binoculars or a telescope.Wondering what other celestial sights you can look forward to this year? Check out this complete list of full moon dates throughout 2021. Time to mark your calendars, skywatchers!