Saturn’s Rings Shine in Webb’s Observations of Ringed Planet

Editor’s Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.

The background is mostly dark. At the center is a dark orange-brownish circle, surrounded by several blazing bright, thick, horizontal whiteish rings. This is Saturn and its rings. There are three tiny organ-like dots in the image—one to the upper left of the planet, one to the direct left of the planet, and the lower left of the planet. They are labeled Dione, Enceladus, and Tethys. There is a slightly darker tint at the northern and southern poles of the planet. The rings surrounding Saturn are mostly broad, with a few singular narrow gaps between the broader rings. At the right side of the planet, labels are applied to the rings. The innermost, thicker ring is labeled “C ring.” Next to that, a brighter, wider ring is labeled “B ring.” Traveling farther outward, a small dark gap is labeled “Cassini division” before another thicker ring labeled “A ring.” Within the “A ring,” a narrow faint band is labeled “Encke gap.” The outermost, faintest, thinnest ring is labeled “F ring.”
Image of Saturn and some of its moons, captured by the James Webb Space Telescope’s NIRCam instrument on June 25, 2023. In this monochrome image, NIRCam filter F323N (3.23 microns) was color mapped with an orange hue. Download the full-resolution image, both labeled and unlabeled, from the Space Telescope Science Institute. Credits: NASA, ESA, CSA, STScI, M. Tiscareno (SETI Institute), M. Hedman (University of Idaho), M. El Moutamid (Cornell University), M. Showalter (SETI Institute), L. Fletcher (University of Leicester), H. Hammel (AURA); image processing by J. DePasquale (STScI)

On June 25, 2023, NASA’s James Webb Space Telescope turned to famed ringed world Saturn for its first near-infrared observations of the planet. The initial imagery from Webb’s NIRCam (Near-Infrared Camera) is already fascinating researchers.

Saturn itself appears extremely dark at this infrared wavelength observed by the telescope, as methane gas absorbs almost all of the sunlight falling on the atmosphere. However, the icy rings stay relatively bright, leading to the unusual appearance of Saturn in the Webb image.

This image was taken as part of Webb Guaranteed Time Observation program 1247. The program included several very deep exposures of Saturn, which were designed to test the telescope’s capacity to detect faint moons around the planet and its bright rings. Any newly discovered moons could help scientists put together a more complete picture of the current system of Saturn, as well as its past.

This new image of Saturn clearly shows details within the planet’s ring system, along with several of the planet’s moons – Dione, Enceladus, and Tethys. Additional deeper exposures (not shown here) will allow the team to probe some of the planet’s fainter rings, not visible in this image, including the thin G ring and the diffuse E ring. Saturn’s rings are made up of an array of rocky and icy fragments – the particles range in size from smaller than a grain of sand to a few as large as mountains on Earth. Researchers recently used Webb to explore Enceladus, and found a large plume jetting from the southern pole of the moon that contains both particles and plentiful amounts of water vapor – this plume feeds Saturn’s E ring.

Saturn’s atmosphere also shows surprising and unexpected detail. Although the Cassini spacecraft observed the atmosphere at greater clarity, this is the first time that the planet’s atmosphere has been seen with this clarity at this particular wavelength (3.23 microns), which is unique to Webb. The large, dark, diffuse structures in the northern hemisphere do not follow the planet’s lines of latitude, so this image is lacking the familiar striped appearance that is typically seen from Saturn’s deeper atmospheric layers. The patchiness is reminiscent of large-scale planetary waves in the stratospheric aerosols high above the main clouds, potentially similar to those seen in early Webb NIRCam observations of Jupiter.

When comparing the northern and southern poles of the planet in this image, the differences in appearance are typical with known seasonal changes on Saturn. For example, Saturn is currently experiencing northern summertime, with the southern hemisphere emerging from the darkness at the end of a winter. However, the northern pole is particularly dark, perhaps due to an unknown seasonal process affecting polar aerosols in particular. A tiny hint of brightening towards the edge of Saturn’s disk might be due to high-altitude methane fluorescence (the process of emitting light after absorbing light), emission from the trihydrogen ion (H3+) in the ionosphere, or both; spectroscopy from Webb could help confirm this.

Missions like NASA’s Pioneer 11, Voyagers 1 and 2, the Cassini spacecraft, and the Hubble Space Telescope have tracked Saturn’s atmosphere and rings for many decades. These observations from Webb are just a hint at what this observatory will add to Saturn’s story in the coming years as the science team delves deep into the data to prepare peer-reviewed results. 

Science Credits

NASA, ESA, CSA, STScI, Matt Tiscareno (SETI Institute), Matt Hedman (University of Idaho), Maryame El Moutamid (Cornell University), Mark Showalter (SETI Institute), Leigh Fletcher (University of Leicester), Heidi Hammel (AURA)

Image Processing Credits

J. DePasquale (STScI)

About the Authors

  • Heidi B. Hammel is a Webb interdisciplinary scientist leading Webb’s Cycle 1 Guaranteed Time Observations (GTO) of the solar system. She is the vice president for science at the Association of Universities for Research in Astronomy (AURA) in Washington, D.C.
  • Leigh Fletcher is a professor of planetary science at the University of Leicester in England. Leigh is the principal investigator for several of Webb’s Guaranteed Time Observation Programs, including Program 1247 highlighted here.
  • Matt Tiscareno is a Senior Research Scientist at the SETI Institute, California, where he studies the dynamics of planetary systems, including planetary rings. He is an integral member of the Webb Guaranteed Time Observation team for the study of Saturn.

Unannotated Version of Image:

The background is mostly dark. At the center is a dark orange-brownish circle, surrounded by several blazing bright, thick, horizontal whiteish rings. This is Saturn and its rings. There are three tiny organ-like dots in the image—one to the upper left of the planet, one to the direct left of the planet, and the lower left of the planet. There is a slightly darker tint at the northern and southern poles of the planet. The rings surrounding Saturn are mostly broad, with a few singular narrow gaps between the broader rings. There is an innermost, thicker ring, and next to that is a brighter, wider ring. Traveling farther outward, there is a small dark gap before another thicker ring. In the thicker ring, there is a narrow faint band. There is then an outermost, faintest, thinnest ring.
Download the full-resolution image, both labeled and unlabeled, from the Space Telescope Science Institute.