The search for biosignatures in Enceladus’ plumes

What kind of mission would be best suited to sample the plumes of Saturn’s ocean world, Enceladus, to determine if this intriguing world has the ingredients to harbor life? This is what a recent study presented at the 56th Lunar and Planetary Science Conference (LPSC 2025) hopes to address as a team of researchers investigated the pros and cons of an orbiter or flyby mission to sample Enceladus’ plumes.

This study has the potential to help scientists, engineers, and mission planners design and develop the most scientifically effective mission to Enceladus with the goal of determining its potential habitability.

Here, Universe Today discusses this incredible research with Dr. Morgan Cable, who is a research scientist in the Laboratory Studies group at the NASA Jet Propulsion Laboratory, regarding the motivation behind the study, significant takeaways, how this proposed mission will compare to Cassini, next steps for developing such a mission, and what forms of life we might find on Enceladus. Therefore, what was the motivation behind the study?

“Enceladus is unique in that material from its subsurface ocean can be accessed without the need to dig, drill or even land,” Dr. Cable tells Universe Today. “This is not something you can do on other planetary bodies, and it’s all thanks to the plume emanating from four giant fissures in the south pole. A spacecraft doing a flythrough of the plume, either from Saturn orbit or via Enceladus orbit, could collect both gas and ice grains and perform measurements to better constrain the habitability of the subsurface ocean and potentially search for evidence of life.”

For the study, the researchers discussed the motivation and variety of reasons why sampling Enceladus’ plumes would produce the most valuable science for studying this ocean world. This included the benefits of a plume-focused mission as opposed to a lander or other type of scientific mission how data obtained by NASA’s Cassini spacecraft contributed to recent discoveries regarding Enceladus. Finally, they discussed the benefits of a flyby versus Enceladus orbiter and the challenges of performing such a daring mission.

The discussion was complemented by the researchers presenting models from previous studies that estimated the salt content of the grains that could potentially be sampled from Enceladus’ plumes. While one study estimated collecting salt-rich grains, the other study estimated collecting grains with less salt.

By combining the two studies, the researchers of this recent study concluded that 100 times more material will need to be collected than previously estimated to obtain sufficient data regarding the contents of Enceladus’ subsurface ocean. Therefore, what are the most significant takeaways from this study?

“Enceladus is the only confirmed body in the solar system where we have access to fresh material from a habitable subsurface ocean,” Dr. Cable tells Universe Today. “We also at a point for the first time in human history where we have developed instruments that can fit on spacecraft and are sufficiently sensitive that, even if there is a single alien microbe entrained within an ice grain in the plume, we could detect it.

“While we certainly started the journey to search for life elsewhere with the Viking missions to Mars, we now may be embarking on the golden era of the search for life in our own cosmic backyard.”

While Cassini was technically designated as an orbiter since it orbited Saturn several times while conducting countless flybys of its many moons, including 11 of Enceladus, it did not enter Enceladus’ orbit to conduct an in-depth analysis of the ocean world and its surface. The only other missions that briefly explored Saturn and its moons were Pioneer 11 and Voyager 1 and 2, all of which conducted flybys of the Saturn system.

As noted, this study builds off data collected by NASA’s Cassini mission that conducted groundbreaking science for over 13 years (2004 to 2017) while orbiting Saturn and its many moons. During this time, Cassini discovered Enceladus’ plumes and even flew through them several times, obtaining data regarding the chemical compositions and grain sizes.

While these plume samples revealed the presence of organic materials, carbon monoxide, carbon dioxide, water vapor, and volatile gases, Cassini’s instruments were not equipped to conduct an in-depth analysis of ice grains. Therefore, how will this proposed orbiter/flyby mission compare to Cassini’s results when it flew through Enceladus’ plumes?

“Cassini’s instruments were state-of-the-art at the time that spacecraft was built and launched; those instruments were also not meant to search for biosignatures or complex organic chemistry,” Dr. Cable tells Universe Today. “With modern instrumentation, we can better identify both small molecules and complex organics, even up to biomolecules such as lipids, polypeptides, DNA or RNA. This is because modern instruments have better mass range and resolution, as well as sensitivity (so even if the molecules are dilute, we can detect them) and the ability to more robustly handle interferents.”

NASA missions typically take several years to go from a concept to launch and often several more years before finally collecting valuable science. For example, while Cassini was launched in 1997, it was actually introduced in 1982 by a working group between the National Academy of Sciences and the European Science Foundation, hence why Cassini was a joint mission between NASA, the European Space Agency (ESA), and the Italian Space Agency.

The next several years consisted of further discussions and some political bumps as the U.S. Congress came close to canceling the project, but NASA persuaded them to stay the course. After launching in 1997, Cassini spent close to seven years traveling to Saturn before officially entering orbit in 2004, followed by spending until 2017 collecting groundbreaking science about Saturn and its many moons. Therefore, what are the next steps for developing this potential orbiter/flyby to sample Enceladus’ plumes?

Dr. Cable tells Universe Today, “The recent Planetary Science and Astrobiology Decadal Survey recommended that Enceladus be included as a potential destination through the New Frontiers Program and also recommended that an Enceladus Orbilander follow Uranus Orbiter and Probe (UOP) as the next-priority flagship mission. So, I imagine one or more mission concept proposals may be submitted to the next New Frontiers call to explore Enceladus, and if selected, that would be very exciting. If not, there is significant community support for a flagship, but after UOP.”

Enceladus is one of the most intriguing and mysterious worlds in our solar system with its plumes of water ice being ejected from its subsurface ocean via cracks in its south pole. But it’s this subsurface ocean that causes the greatest amount of intrigue, as Earth demonstrates liquid water is one of the key ingredients for life as we know it, providing millions of aquatic species of all shapes and sizes.

An Earth analogy for what scientists could find on Enceladus are hydrothermal vents, which are found near regions of volcanic activity at the bottom of the ocean. These vents often consist of black smokers and white smokers, with each discharging their own respective set of minerals and ecosystems. Some examples of life found at hydrothermal vents include crabs, shrimp, tube worms, and mussels. Therefore, what forms of life do Dr. Cable think we could find in Enceladus?

“Based on our understanding of the amount of energy available in the ocean, it’s not likely that the density of life is very high,” Dr. Cable tells Universe Today. “In Earth’s oceans, where sunlight (our primary energy source) is abundant, we see cell densities on the order of 100,000–1,000,000 cells per milliliter of ocean water, which can support organisms as large as fish, sharks and whales. In energy-limited environments, such as the ice-covered lakes of Antarctica (which don’t have access to sunlight), we tend to see cell densities on the order of 100–1,000 cells per milliliter.”

Dr. Cable continues, “And that I think is more likely at Enceladus, as sunlight won’t be an option in the ocean underneath the ice shell; the primary energy source is likely to be hydrothermal energy at the seafloor. But that doesn’t mean necessarily we’ll only see microbes. On Earth, at hydrothermal vents at our seafloor, we see diverse communities that include shrimp, octopods and other multicellular organisms, so we can’t rule that out. I think we’ll be excited no matter what we find.”

Other ocean worlds of intrigue include Saturn’s largest moon, Titan; Jupiter’s moons, Europa, Ganymede, and Callisto; Uranus’ moons, Ariel, Umbriel, Oberon, and Titania; Neptune’s moon, Triton; and even dwarf planets Pluto and Ceres. Europa is being visited by NASA’s Europa Clipper to examine its subsurface ocean while NASA’s Juno continues to study Europa and the other Galilean moons. For Titan, NASA is slated to launch its Dragonfly quadcopter in 2028 with an estimated arrival at Titan in 2034.

For now, a future Enceladus mission continues to be on the drawing board with the Enceladus Orbilander being the most anticipated mission to explore Enceladus and its subsurface ocean while researchers continue to ponder whether life as we know it, or even as we don’t know it, could exist within its watery depths.

Dr. Cable tells Universe Today, “One of the most interesting parts of my research is the opportunity to work and interact with people from a multitude of different disciplines, ranging from chemistry and geophysics to marine biology and oceanography. So, I think it’s important to realize that you can study something pretty far removed from astrophysics or astronomy and still potentially join a mission team to explore big questions about our universe.”

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