The Cassini space probe ended its mission in 2017 with a dramatic plunge into Saturn, yet it continues to fuel discoveries.

In a new analysis of data from one of the probe’s instruments, an international team of researchers has identified new organic compounds within jets of icy water erupting from Saturn’s moon, Enceladus. The material likely originated in Enceladus’ ocean, and adds to mounting evidence that the moon could be habitable.

“We found a rich organic inventory in Enceladus’ plume,” said Fabian Klenner, a 91Ě˝»¨ postdoctoral researcher of Earth and space sciences and a member of the research team. “Having clear evidence of a variety of organic compounds from inside an extraterrestrial water world is incredible and further strengthens Enceladus’ potential for habitability. It appears that Enceladus has all the ingredients for life as we know it.”

in Nature Astronomy.

Launched in 1997, Cassini performed a while in orbit around Saturn, resolving two longstanding mysteries surrounding the system: the origin of Saturn’s enormous but faint E ring and the cause of Enceladus’ unusual brightness. Enceladus, it turns out, is covered in a 16-19 miles thick shell of highly reflective ice which hides a global saltwater ocean. The probe observed fissures in the ice of the moon’s South Polar Terrain ejecting massive quantities of icy water into space. Some of the material forms Saturn’s E ring.

Data from Cassini’s Cosmic Dust Analyzer, or CDA, previously helped researchers identify organic compounds and other key building blocks for life within Saturn’s E ring. Cassini also found material in the E ring that suggests hydrothermal activity deep within Enceladus.

“We suspect that so-called hydrothermal fields exist there — these are vents at the bottom of the ocean from which hot water rises. There is evidence that life on Earth originated in such fields,” said lead author , a research group leader at Freie Universität Berlin.

The new results come from data collected in a close flyby of Enceladus’ icy plume, offering scientists a look at material that had been inside the moon just minutes before.

“The high-speed flyby of Enceladus enabled us to identify new compounds that were not found in the E ring data, most notably esters, alkenes and ether compounds,” said Klenner, who helped validate the new CDA results. “Notably, esters and ethers can be part of lipids, and lipids are key to life as we know it.”

The success of Cassini has helped stoke considerable investment in future missions to the outer solar system. ±·´ˇł§´ˇâ€™s is currently en route to Jupiter to study its moon Europa, which is also a promising candidate in the search for extraterrestrial life.

In the meantime, there’s plenty more Cassini data up for grabs.

“It’s phenomenal to continue learning from the Cassini mission,” said Klenner, who will start a new position as an assistant professor at the University of California, Riverside in December. “Much of the CDA data still isn’t analyzed and I’m so excited about what it may reveal next.”

Co-authors include , , , and at Freie Universität Berlin; at the University of Colorado, Boulder; and at the Institute of Science Tokyo; and and at the University of Stuttgart.Ěý

This research was funded by the European Research Council, the German Aerospace Center, the state of Berlin and NASA.

For more information, contact Klenner at fklenner@uw.edu.Ěý

This story was adapted by the University of Stuttgart.

The ice-encrusted oceans of some of the moons orbiting Saturn and Jupiter are leading candidates in the search for extraterrestrial life. A new lab-based study led by the 91Ě˝»¨ in Seattle and the Freie Universität Berlin shows that individual ice grains ejected from these planetary bodies may contain enough material for instruments headed there in the fall to detect signs of life, if such life exists.

“For the first time we have shown that even a tiny fraction of cellular material could be identified by a mass spectrometer onboard a spacecraft,” said lead author , a 91Ě˝»¨postdoctoral researcher in Earth and space sciences. “Our results give us more confidence that using upcoming instruments, we will be able to detect lifeforms similar to those on Earth, which we increasingly believe could be present on ocean-bearing moons.”

The open-access was published March 22 in Science Advances. Other authors in the international team are from The Open University in the U.K.; ±·´ˇł§´ˇâ€™s Jet Propulsion Laboratory; the University of Colorado, Boulder; and the University of Leipzig.

The Cassini mission that ended in 2017 discovered parallel cracks near the south pole of Saturn’s moon Enceladus. Emanating from these cracks are plumes containing gas and ice grains. ±·´ˇł§´ˇâ€™s mission, scheduled to launch in October, will carry more instruments to explore in even more detail an icy moon of Jupiter, Europa.

To prepare for that mission, researchers are studying what this new generation of instruments might find. It is technically prohibitive to directly simulate grains of ice flying through space at 4 to 6 kilometers per second to hit an observational instrument, as the actual collision speed will be. Instead, the authors used an experimental setup that sends a thin beam of liquid water into a vacuum, where it disintegrates into droplets. They then used a laser beam to excite the droplets and mass spectral analysis to mimic what instruments on the space probe will detect.

Newly published results show that instruments slated to go on future missions, like the onboard Europa Clipper, can detect cellular material in one out of hundreds of thousands of ice grains.

The study focused on Sphingopyxis alaskensis, a common bacterium in waters off Alaska. While many studies use the bacterium Escherichia coli as a model organism, this single-celled organism is much smaller, lives in cold environments, and can survive with few nutrients. All these things make it a better candidate for the kinds of life that may exist on the icy moons of Saturn or Jupiter.

“They are extremely small, so they are in theory capable of fitting into ice grains that are emitted from an ocean world like Enceladus or Europa,” Klenner said.

Results show that the instruments can detect this bacterium, or portions of it, in a single ice grain. Different molecules end up in different ice grains. The new research shows that analyzing single ice grains, where biomaterial may be concentrated, is more successful than averaging across a larger sample containing billions of individual grains.

A recent study led by the same researchers showed evidence of phosphate on Enceladus. This planetary body now appears to contain energy, water, phosphate, other salts and carbon-based organic material, making it increasingly likely to support lifeforms similar to those found on Earth.

The authors hypothesize that if bacterial cells are encased in a lipid membrane, like those on Earth, then they would also form a skin on the ocean’s surface. On Earth, ocean scum is a key part of sea spray that contributes to the smell of the ocean. On an icy moon where the ocean is connected to the surface, for example through cracks in the ice shell, the vacuum of outer space would cause this subsurface ocean to boil. Gas bubbles rise through the ocean and burst at the surface, where cellular material gets incorporated into ice grains within the plume.

“We here describe a plausible scenario for how bacterial cells can, in theory, be incorporated into icy material that is formed from liquid water on Enceladus or Europa and then gets emitted into space,” Klenner said.

The SUrface Dust Analyzer onboard Europa Clipper will be higher-powered than instruments on past missions. This and future instruments also will for the first time be able to detect ions with negative charges, making them better suited to detecting fatty acids and lipids.

“For me, it is even more exciting to look for lipids or for fatty acids, than to look for building blocks of DNA, and the reason is because fatty acids appear to be more stable,” Klenner said.

“With suitable instrumentation, such as the SUrface Dust Analyzer on ±·´ˇł§´ˇâ€™s Europa Clipper space probe, it might be easier than we thought to find life, or traces of it, on icy moons,” said senior co-author , a professor of planetary sciences at the Freie Universität Berlin. “If life is present there, of course, and cares to be enclosed in ice grains originating from an environment such as a subsurface water reservoir.”

The study was funded by the European Research Council, NASA and the German Research Foundation (DFG). Other co-authors are Janine Bönigk, Maryse Napoleoni, Jon Hillier and Nozair Khawaja at the Freie Universität Berlin; Karen Olsson-Francis at The Open University in the U.K.; Morgan Cable and Michael Malaska at the NASA Jet Propulsion Laboratory; Sascha Kempf at the University of Colorado, Boulder; and Bernd Abel at the University of Leipzig.

For more information, contact Klenner at fklenner@uw.edu (based in Seattle) or Postberg at frank.postberg@fu-berlin.de (based in Berlin).

An international team including a 91Ě˝»¨ scientist has found that the water on one of Saturn’s moons harbors phosphates, a key building block of life. The team led by the Freie Universität Berlin used data from ±·´ˇł§´ˇâ€™s Cassini space mission to detect evidence of phosphates in particles ejected from the ice-covered global ocean of Saturn’s moon Enceladus.

Phosphorus, in the form of phosphates, is vital for all life on Earth. It forms the backbone of DNA and is part of cell membranes and bones. The new , published June 14 in Nature, is the first to report direct evidence of phosphorus on an extraterrestrial ocean world.

The team found that phosphate is present in Enceladus’ ocean at levels at least 100 times higher — and perhaps a thousand times higher — than in Earth’s oceans.

“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 third author , a 91Ě˝»¨postdoctoral researcher in Earth and space sciences. While at Freie Universität Berlin, Klenner did experiments that revealed the high phosphate concentrations present in Enceladus’ ocean.

One of the most profound discoveries in planetary science over the past 25 years is that worlds with oceans beneath a surface layer of ice are common in our solar system. These ice-covered celestial bodies include the icy moons of Jupiter and Saturn — including Ganymede, Titan and Enceladus — as well as even more distant celestial bodies, like Pluto.

±·´ˇł§´ˇâ€™s explored Saturn, its rings and its moons from 2004 to 2017. It first discovered that Enceladus’ harbors an ice-covered watery ocean, and analyzed material that erupted through cracks in the region of the moon’s south pole.

The spacecraft was equipped with the . which analyzed individual ice grains emitted from Enceladus and sent those measurements back to Earth. To determine the chemical composition of the grains, Klenner used a specialized setup in Berlin that mimicked the data generated by an ice grain hitting the instrument. He tried different chemical compositions and concentrations for his samples to try to match the unknown signatures in the spacecraft’s observations.

“I prepared different phosphate solutions, and did the measurements, and we hit the bullseye. This was in perfect match with the data from space,” Klenner said. “This is the first finding of phosphorus on an extraterrestrial ocean world.”

Planets with surface oceans, like Earth, must reside within a narrow range of distances from their host stars (in what is known as the “habitable zone”) to maintain temperatures at which water neither evaporates nor freezes. Worlds with an interior ocean like Enceladus, however, can occur over a much wider range of distances, greatly expanding the number of habitable worlds likely to exist across the galaxy.

In previous studies, the team at the Freie Universität Berlin determined that Enceladus harbors a “soda ocean,” rich in dissolved carbonates, that also contains a vast variety of reactive and sometimes complex carbon-containing compounds. The team also found indications of hydrothermal environments on the seafloor.Ěý The new study now shows the unmistakable signatures of dissolved phosphates.

“Previous geochemical models were divided on the question of whether Enceladus’ ocean contains significant quantities of phosphates at all,” said lead author at Freie Universität Berlin. “These measurements leave no doubt that substantial quantities of this essential substance are present in the ocean water.”

To investigate how the ocean on Enceladus can maintain such high concentrations of phosphate, geochemical lab experiments and modeling included in the new paper were conducted by a Japan-based team led by second author at the Tokyo Institute of Technology and a U.S.-based team led by fourth author at the Southwest Research Institute in San Antonio, Texas. Other authors are from Germany, the U.S., Japan and Finland.

For more information, contact Klenner at fklenner@uw.edu and Postberg at frank.postberg@fu-berlin.de.

Adapted from a Freie Universität Berlin .