The Cassini spacecraft passes through jets emanating from Saturn’s moon Enceladus (artist’s impression).Credit: NASA/JPL-Caltech
The James Webb Space Telescope (JWST) has spotted Saturn’s moon Enceladus spewing out a huge plume of water vapor far larger than any seen there before. This huge cloud may contain the chemical ingredients of life that have escaped from beneath the moon’s icy surface.
In 2005, a NASA spacecraft called Cassini discovered ice particles pouring out of Enceladus’ subsurface ocean through cracks in the moon’s surface. But JWST shows that the material is spewing much farther than previously thought — many times deeper into space than the size of Enceladus itself.
“It’s huge,” Sarah Fagy, a planetary astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said May 17 at a conference at the Space Telescope Science Institute in Baltimore, Maryland. She declined to provide further details, citing a soon-to-be-published scientific paper.
A rare ocean world
Enceladus excites astrobiologists because it is one of the few “ocean worlds” in the Solar System, making it one of the best places to look for extraterrestrial life. The salty ocean that lies beneath Enceladus’ outer icy shell is a possible refuge for living organisms that can be sustained by chemical energy in hydrothermal vents on the ocean floor.
The material that flows out of Enceladus, primarily through fractures known as tiger stripes around the moon’s south pole, is a direct link to this potential alien ecosystem. The plumes seen by Cassini contain particles of silica that were likely carried from the seafloor by boiling fluids1. Cassini flew through Enceladus’ jets many times, measuring ice grains and life-supporting chemicals such as methane, carbon dioxide and ammonia.
But it took JWST, a telescope 1.5 million kilometers from Earth, to detect something Cassini couldn’t see from its ringside seat. While Cassini can spot ice grains that don’t travel far from the surface, JWST has a wider perspective and sensitive instruments that can pick up faint gas signals around Enceladus.
Enceladus at a glance
On November 9, 2022, JWST took a brief peek at Enceladus. Just 4.5 minutes of data revealed the huge, very cold cloud of water vapor. The upcoming paper will quantify how much water is sprayed and its temperature, Fagy said. But the jet is likely to be low-density, more like a diffuse, cold cloud than a wet spray. This is not good news for anyone who wants to sample the cloud and hope to find life, as signs of life may be too scarce to detect2. Ice grains observed by Cassini much closer to Enceladus are more likely to have high concentrations of organic particles, says Shannon McKenzie, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland.
Scientists have created a new type of ice that could exist on distant moons
JWST also analyzed the spectrum of sunlight reflected from Enceladus and found evidence of many chemicals, including water and possibly other compounds, that could hint at geological or biological activity in the moon’s ocean. “We have a lot more surprises in store,” Fagy said.
The researchers are already planning how to continue the discovery. Last week, JWST organizers released a list of observations to be made in the telescope’s second round of operations — and it includes another project to study Enceladus. This work will look at Enceladus six times longer than the first JWST survey and will aim to find chemical compounds associated with habitability, such as organic compounds and hydrogen peroxide. “The new observation will give us our best shot at looking for indicators of habitability on the surface,” said project leader Christopher Gline, a geochemist at the Southwest Research Institute in San Antonio, Texas.
A robotic snake for lunar exploration
JWST’s findings provide more basis for a possible NASA mission to Enceladus to search for signs of life there. Proposals under consideration include an “orbilander” mission that would orbit the moon for a year and a half before landing at its south pole. Another proposal calls for the development of an autonomous robotic snake that could slither beneath the ice of Enceladus to explore the ocean.
Other icy moons in the Solar System are also getting attention from JWST. At the conference, Jeronimo Villanueva, a planetary scientist at Goddard, announced that the telescope had detected carbon dioxide on Jupiter’s moon Europa. This excites scientists because carbon and oxygen are key building blocks for life on Earth. NASA is launching a mission to Europa next year that will explore this ocean world in more detail. “This is definitely a new era in solar system exploration,” Villanueva said.
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