NASA’s JWST space telescope has observed a 10,000-kilometer-long plume of water vapor jetting into space from Saturn’s moon Enceladus—the largest spray ever detected from the icy world, which is just one-seventh the diameter of Earth’s Moon.

Planetary scientists view Enceladus as a prime target in the search for extraterrestrial life because beneath its icy crust the moon houses a salty ocean—a good medium for the ingredients of life to mix. Vented from fractures in the crust, the towering plume might saturate the Saturn system with some of the chemicals needed for life. Researchers describe the results today in a NASA press release and in a paper accepted at Nature Astronomy.

“It’s staggering to have such a huge plume from such a small object,” says Christopher Parkinson, a planetary scientist at the California Institute of Technology who was not part of the JWST study.

Parkinson was a research scientist on NASA’s Cassini mission, which in 2005 discovered the plumes on Enceladus. The space probe flew through them seven times during its 13-year mission, discovering organic molecules such as methane and formaldehyde, and hydrogen, a potential energy source for microbes. But models based on Cassini data indicated the plume extended several hundred kilometers into space, not several thousand, Parkinson notes.

JWST observed the vast plume on 9 November 2022 using its high-resolution infrared spectrometer to capture faint fluorescent emissions caused by sunlight striking water molecules near the moon. In just 4.5 minutes, the telescope saw this plume extending about 20 times farther into space than the diameter of Enceladus itself.

As Enceladus whips around Saturn every 33 hours, the plume creates a doughnut-shaped water vapor cloud that feeds one of Saturn’s icy rings. The JWST data also indicate that Enceladus shoots about 300 kilograms of water vapor into space every second, about the same rate that Cassini saw nearly 20 years ago. The plume’s steady activity “only enhances my excitement about going to Enceladus to search for biosignatures,” says Jonathan Lunine, a planetary scientist at Cornell University.

Unlike Cassini, JWST did not find a clear sign of organic compounds during its brief observation. The telescope should have a better chance of searching for them during a roughly 1-hour examination of the plume scheduled for some time during the next yearlong observing cycle, which begins in August, says Geronimo Villanueva, a planetary astronomer at NASA’s Goddard Space Flight Center and co-author on the new study.

The best way to study these organic compounds is to send another spacecraft to Enceladus, Lunine says. He supports a proposed NASA mission called the Enceladus OrbiLander that would orbit and then land on the moon. Cassini directly sampled ice grains and water vapor during its journeys through the plume, but he says a contemporary probe could do much better. “It’s time to go back with state-of-the-art mass spectrometry and other instruments to look for life,” Lunine says. “Let’s go!”

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