May 30, 2023
In a groundbreaking discovery, NASA's James Webb Space Telescope has detected a water vapor plume stretching over 6,000 miles from Saturn's moon Enceladus, which is equivalent to the distance between Los Angeles, California, and Buenos Aires, Argentina. This remarkable finding marks the first time such an extensive water emission has been observed, providing scientists with a direct view of how this plume contributes to the water supply of the entire Saturn system, including its iconic rings.
Enceladus, a captivating ocean world approximately four percent the size of Earth and measuring just 313 miles across, has become one of the most intriguing targets in the search for extraterrestrial life within our solar system. Beneath the moon's icy outer crust and rocky core lies a vast reservoir of salty water. Geysers resembling volcanos eject jets of ice particles, water vapor, and organic chemicals through crevices known informally as "tiger stripes" on the moon's surface.
Previous observations by different observatories have mapped jets of water vapor hundreds of miles from Enceladus' surface. However, the James Webb Space Telescope's extraordinary sensitivity has unveiled an entirely new narrative.
Lead author Geronimo Villanueva from NASA's Goddard Space Flight Center in Greenbelt, Maryland, expressed astonishment at the data, stating, "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. The water plume extends far beyond its release region at the southern pole."
The size of the plume is not the only intriguing characteristic. Researchers are also fascinated by the rate at which water vapor is spewing out: a staggering 79 gallons per second. This extraordinary flow could fill an Olympic-sized swimming pool in just a couple of hours. By comparison, achieving the same volume using a garden hose on Earth would take over two weeks.
While the Cassini orbiter, which spent over a decade exploring the Saturnian system, previously imaged Enceladus' plumes and even flew through them to collect samples, Webb's unique vantage point from the Sun-Earth Lagrange Point 2, situated one million miles from Earth, coupled with the remarkable sensitivity of its Integral Field Unit aboard the NIRSpec (Near-Infrared Spectrograph) Instrument, offers fresh context.
Villanueva explains, "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 donut, in its wake. In the Webb observations, not only was the plume huge, but there was just water absolutely everywhere."
The extensive water distribution observed, described as a torus, is situated in the same region as Saturn's outermost and widest ring, known as the dense "E-ring."
Webb's observations directly illustrate how Enceladus' water vapor plumes contribute to the formation of this torus. By analyzing the Webb data, astronomers have determined that approximately 30 percent of the water remains within the torus, while the remaining 70 percent escapes to supply water to the rest of the Saturnian system.
In the years to come, the James Webb Space Telescope will play a crucial role in studying Enceladus as the primary observational tool. Webb's discoveries will provide vital insights for future missions to explore the moon's subsurface ocean depth, ice crust thickness, and more.
Co-author Stefanie Milam from NASA Goddard remarks, "Right now, Webb provides a unique way to directly measure how water evolves and changes over time across Enceladus' immense plume, and as we see here, we will even make new discoveries and learn more about the composition of the underlying ocean. 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 observations of Enceladus by Webb were conducted as part of the Guaranteed Time Observation (GTO) program 1250. This program aims to demonstrate Webb's capabilities in a specific area of scientific research and pave the way for future studies.
Heidi Hammel, Webb interdisciplinary scientist and leader of the GTO program from the Association of Universities for Research in Astronomy, expresses her excitement, stating, "This program 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."
The team's findings have been accepted for publication in Nature Astronomy, with a pre-print available for reference. This significant discovery opens up new avenues for understanding the dynamics of water on Enceladus and sheds light on the potential for habitability beyond our planet.