Scientists have discovered complex organic molecules in the water plumes of Saturn’s icy moon Enceladus, nearly 20 years after NASA’s Cassini spacecraft first flew through them. These molecules, which contain carbon, are part of the chemical reactions that can lead to the building blocks of life.
Cassini, which concluded its mission in 2017, captured these samples while flying through Enceladus’ plumes and the surrounding E-ring, a diffuse ring formed from material escaping the moon’s surface. The plumes originate from fissures known as “tiger stripes” that are believed to connect to a subsurface ocean beneath Enceladus’ 310-mile-wide (500-kilometer-wide) surface.
While previous studies had detected organic molecules in the E-ring, scientists remained uncertain whether they came from Enceladus’ ocean or were created by radiation reactions in Saturn’s magnetosphere. To clarify this, Nozair Khawaja and his team at Freie Universität Berlin and the University of Stuttgart revisited Cassini’s 2008 Cosmic Dust Analyzer (CDA) data.
“When ice grains from the plumes hit the CDA at higher speeds, we can detect organic molecules that would otherwise be hidden in slower impacts,” Khawaja explained. The team’s reanalysis revealed the same organics in the plumes as those found in the E-ring, confirming that they originate from the subsurface ocean rather than radiation-induced reactions in space.
Additionally, the study uncovered several previously undetected molecules, including aliphatics, heterocyclic compounds, esters, ethers, and potentially nitrogen- and oxygen-bearing compounds—chemicals that on Earth participate in reactions leading to life. “These findings increase the likelihood that Enceladus could be habitable,” said Khawaja.
However, caution remains. Research led by Grace Richards at the Istituto Nazionale di Astrofisica e Planetologia Spaziale suggests that radiation at the surface, especially near the tiger stripes, could also generate organic molecules. This makes it challenging to determine definitively whether the detected organics truly come from the ocean.
The most conclusive way to resolve this uncertainty would be to directly sample fresh ice on Enceladus, a goal the European Space Agency may pursue with a proposed orbiter-lander mission scheduled for 2054.
The latest results from Cassini’s Cosmic Dust Analyzer were published on October 1 in Nature Astronomy.
