A Saturn moon's ocean may have the chemistry to start life

A moon of Saturn has a surprising variety of carbon-based molecules that look like they were made in its hidden ocean — the kind of environment where life might begin, new research reveals.

NASA's Cassini spacecraft flew through the enormous geysers spurting out of Enceladus in 2008. Those plumes, soaring 6,000 miles above the moon's icy crust, harbor water and salts but also a mix of complex carbon-based molecules. These include chemicals that, on Earth, often come from hot water-rock reactions near seafloor vents, where many scientists believe the origins of life started for this planet. 

Cassini had previously detected tiny ice grains in Saturn's rings that contained organic molecules and precursors to amino acids, the molecules that build proteins. Scientists have long believed Saturn's so-called "E ring" material comes from Enceladus. But those samples could have been hundreds of years old and altered by cosmic radiation. They needed more pristine samples taken from closer to the source. 

Nozair Khawaja, lead author of the new study published in Nature Astronomy, said the data already existed but wasn't fully understood yet.

"With more knowledge, experience, and experiments, we reanalyzed the flyby data in more detail and understood features that we detected (in this work) for the first time," Khawaja told Mashable. 

Researchers say the discovered organics most likely came from Enceladus' ocean floor, not from space contamination. Cassini sampled the fresh grains with its Cosmic Dust Analyzer instrument within minutes of Enceladus ejecting them. The data was captured during the spacecraft's fastest flyby of over 40,000 mph. 

That superfast speed gives the team more confidence in the findings because particles smash apart differently at that rate, making detection of organic molecules easier, said Khawaja, a Freie Universität Berlin scientist. 

Researchers have detected brand-new organic compounds in Enceladus' plumes that suggest the moon's ocean chemistry is more complex than anyone knew. Credit: NASA / JPL-Caltech / Space Science Institute

After recreating the ice grains hitting the detector at high versus low speeds in a lab, they got matching results. This means the chemical signals the scientists saw weren't caused by the collision but were actual features of the molecules, he said.

The new research compared the organic molecules previously detected in Saturn's E ring with the fresh ice grains, and found they were consistent, supporting the idea that the ring's material is coming from the moon's underground ocean. 

The team also has detected brand-new organic compounds, showing that Enceladus' ocean chemistry is more complex than anyone knew. The researchers found ring-shaped carbon molecules and oxygen-linked molecules, such as aldehydes, which on Earth can lead to amino acids. There were esters, alkenes, and ethers — chemical types that show up regularly in living things in the form of fats and oils. The grains also contained hints of nitrogen-oxygen compounds, like acetonitrile or pyridine.

Enceladus' plumes appear to feed Saturn's E ring material as it orbits the planet in this Cassini spacecraft image. Credit: NASA / JPL / Space Science Institute

So far Cassini has spotted five of the six key elements needed for Earth life at Enceladus. The missing one is sulfur. The team continues to run lab experiments with sulfur compounds to see if they can match the signals in simulations. It could be that sulfur is just a harder ingredient to detect.

The study's results bolster ESA's plans for a follow-up mission to orbit and land on Enceladus in the future.

"This further enhances the habitability potential,"  Khawaja said, "further driving the need for a new mission."