Fascinating Plumes

Saturn's moon Enceladus has complex, life-friendly chemistry

- Jacek Krywko

Artist's depiction of Cassini sampling plumes from the subsurface ocean of Saturn's icy moon Enceladus

ENCELADUS, a 500-kilometer-wide moon of Saturn, has been a top target in the hunt for extraterrestrial life for nearly two decades. In 2005, shortly after arriving in orbit around the ringed planet, the joint NASA-European Space Agency (ESA) Cassini mission found plumes of water spraying up from Enceladus's south pole—clinching evidence that the moon harbored a liquid-water ocean underneath its bright-white icy crust. Astrobiologists have become ever more enthralled by Enceladus as further studies of the plumes' ice grains have revealed multiple molecular building blocks of life blasting out from the hidden ocean.

Now scientists revisiting data from Cassini, which ended its mission to Saturn in 2017, have spied even more tantalizing ingredients in the plumes: suites of complex organic molecules that, on Earth, are involved in the chemistry associated with even bigger compounds considered essential for biology. The discovery, published in Nature Astronomy, bolsters the case for followup missions to search for signs of life within this enigmatic moon.

Its remoteness from Earth isn't the only thing that has let Enceladus keep so many secrets for so long. The Cassini orbiter wasn't really designed for deep scrutiny of a single, specific object in Saturn's system, says Nozair Khawaja, a planetary scientist at the Free University of Berlin, who led the Nature Astronomy study. Cassini launched nearly 30 years ago, back when Enceladus's subsurface ocean and south polar plumes were unknown. Repurposing its vintage kit for in-depth astrobiology was difficult—not least because of how hard the resulting data were to work with.