A toxic gas that could help spawn life has been found on Enceladus

The moon’s water plume contains hydrogen cyanide, an analysis of Cassini data suggests

A photo of jets of water vapor erupting on the surface of Enceladus.

In 2005, Cassini discovered jets of water (shown) erupting from Enceladus’ surface. The spacecraft later flew through the plume of material formed by the jets multiple times, measuring the plume’s composition and detecting chemical ingredients for life.


SAN FRANCISCO — For those delighted by the possibility of alien life, Enceladus, the wintry moon of Saturn, is a gift that just keeps giving.

Key compounds that could support alien microbes or help life emerge have been detected in the enormous plume of water that erupts from vents in Enceladus’ icy shell, biophysicist Jonah Peter of Harvard University reported December 15 at the American Geophysical Union annual meeting. These include hydrogen cyanide, which can be toxic to humans, though Peter noted it’s also “a key building block for synthesizing more complex compounds including amino acids, sugars and nucleobases, which in turn are precursors for proteins, RNA and DNA.”

The findings are good tidings for the NASA team developing the Exobiology Extant Life Surveyor, or EELS, a snakelike robot that could one day crawl into Enceladus’ frozen crust to seek out signs of life in the ocean below.

Though that ocean has never been directly observed, it is thought to be the source of the huge water plume spouting from Enceladus’ south pole (SN: 6/9/23). Researchers had previously reported that the plume contains phosphorous in the form of phosphate, establishing Enceladus as the first alien ocean world known to possess all the elements essential for life (SN: 12/16/23). The detection of phosphorus bolstered the moon as a prime candidate for hosting extraterrestrial life, and the new findings from Peter’s team offer even more support.

With hydrogen cyanide and phosphate, “Enceladus might be seen as a favorable prebiotic system,” or a chemical setting capable of giving rise to life, said Christopher Glein, a geochemist at the Southwest Research Institute in San Antonio who was not involved in the study.

Peter and colleagues conducted a detailed analysis of data collected by NASA’s Cassini probe as it flew through Enceladus’ plume in 2011 and 2012. In addition to hydrogen cyanide, the spray contains acetylene, ethane and various alcohols, the team also reported December 14 in Nature Astronomy. These compounds fuel some microbes on Earth, Peter said, “and could supply large amounts of metabolic energy for any potential life” on Enceladus.

Though NASA has no missions scheduled for Enceladus, its habitability has already spurred the development of EELS. The 100-kilogram, 4-meter-long robot consists of ringed, cylindrical segments. These pieces can be angled and rotated in different ways to make EELS slither, sidewind or move vertically inside crevasses.

A photo of a snakelike robot, known as NASA's Exobiology Extant Life Surveyor, resting on the snow.
The EELS robot (seen here) operates on the snow at the Big Bear Mountain Resort in Southern California, during a field test in February 2023.JPL-Caltech/NASA

The robot’s most recent field test occurred in September, on the Athabasca Glacier in Alberta, Canada, reported technologist Masahiro Ono on December 13 at the meeting. On the glacier, Ono, of the Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues tested the vertical mobility of EELS inside three ice shafts, or moulins. The robot first succeeded at holding itself steady in the moulins, unfurling its body to lodge itself between the frozen walls. Then, by carefully rotating treaded rings on its body, EELS safely completed multiple 1.5-meter descents.

Following further tests on the glacier, the next step for EELS might be Earth’s moon. For instance, a small version of the space snake could be deployed to assist stationary lunar landers, Ono said. This robot “is a game changer,” he said, “and not just for Enceladus.”

Nikk Ogasa is a staff writer who focuses on the physical sciences for Science News. He has a master's degree in geology from McGill University, and a master's degree in science communication from the University of California, Santa Cruz.

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