A water vapour plume from Enceladus has been detected by researchers using the James Webb Space Telescope – providing insight into how this feeds Saturn’s entire water supply.
Spanning more than 9,600 kilometres, the observed water plume is the first time such water ejection has been observed over such an expansive distance.
Webb will allow scientists to understand how this emission feeds the water supply for the entire system of Saturn and its rings.
The results of the study, ‘JWST molecular mapping and characterization of Enceladus’ water plume feeding its torus,’ were accepted for publication in Nature Astronomy on 17 May.
About Enceladus
Enceladus is an ocean world around 4% of the size of Earth – just 313 miles across. The moon is regarded as one of the most exciting scientific targets in our solar system in the search for life beyond Earth.
Located between its icy outer crust and its rocky core is a global reservoir of salt water. Here, volcanos similar to geysers release jets of ice particles, water vapour, and organic chemics out of crevices in the moon’s surface.
Previously, it was believed that the water plumes were located hundreds of miles from the moon’s surface. However, Webb’s sensitivity has now provided new findings.
The detected water plume is more than 20 times the size of the moon
“When I was looking at the data, at first, I was thinking I had to be wrong. It was just so shocking to detect a water plume more than 20 times the size of the moon,” said lead author Geronimo Villanueva of NASA’s Goddard Space Flight Centre in Greenbelt, Maryland. “The water plume extends far beyond its release region at the southern pole.”
It was not only the plume’s length that intrigued researchers. The rate at which the water vapour is gushing out, about 79 gallons per second, is also impressive. An Olympic-sized swimming pool could be filled up in a couple of hours at this extraordinary rate, whereas it would take over two weeks to do so with a garden hose.
Webb’s observation shows how the moon’s water vapour plumes feed the torus
For over a decade, the Cassini orbiter explored Saturn. During this time, it not only imaged the plumes of Enceladus but also flew directly through them and sampled what they were made of. Cassini’s position within the Saturnian system provided invaluable insights into the moon.
Webb’s unique view further offered a new context. Located on the Sun-Earth Lagrange Point 2, one million miles from Earth, coupled with the sensitivity of its Integral Field Unit aboard the NIRSpec Instrument, Webb demonstrated how the moon’s water plumes feed Saturn.
“The orbit of Enceladus around Saturn is relatively quick, just 33 hours. As it whips around Saturn, the moon and its jets are basically spitting off water, leaving a halo, almost like a doughnut, in its wake,” said Villanueva. “In the Webb observations, not only was the plume huge, but there was just water absolutely everywhere.”
This doughnut is described as a torus and is co-located with Saturn’s outermost and widest ring – the ‘E-ring.’
Astronomers have analysed the Webb data and discovered that around 30% of the water stays within the torus. The other 70% escapes to supply the rest of the Saturnian system of water.
Webb will now serve as the primary observation tool for Enceladus
Webb’s discoveries about Enceladus will help inform solar system satellite missions that will look to explore the subsurface ocean’s depth, how thick the ice crust is, and more.
“Right now, Webb provides a unique way to directly measure how water evolves and changes over time across Enceladus’ immense water plume, and as we see here, we will even make new discoveries and learn more about the composition of the underlying ocean,” added co-author Stefanie Milam at NASA Goddard.
“Because of Webb’s wavelength coverage and sensitivity, and what we’ve learned from previous missions, we have an entire new window of opportunity in front of us.”
The James Webb Space Telescope’s observations of Enceladus were completed under Guaranteed Time Observation (GTO) programme 1250. The programme’s initial goal is to demonstrate the capabilities of Webb, setting the scene for future studies.
“This programme was essentially a proof of concept after many years of developing the observatory, and it’s just thrilling that all this science has already come out of quite a short amount of observation time,” said Heidi Hammel of the Association of Universities for Research in Astronomy, Webb interdisciplinary scientist and leader of the GTO programme.
