Credit: NASA, ESA, CSA, JWST Saturn Team, Joseph Depasquale (STScI)

JWST turned to the ringed world Saturn in June 2023 to conduct a deep search for new ring structure and faint moons. Saturn itself appears to extremely dark at the infrared wavelengths sensed by JWST’s Near-Infrared Camera (NIRCam), 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 JWST image.

Several very deep Saturn exposures taken together with this image were designed to test JWST’s capacity to detect faint moons around the planet and its bright rings. Any newly discovered moons would be important dynamical tracers of the current Saturn system as well as its past history. This context image clearly shows details within the ring system, along with many of Saturn’s moons. The team will use this context image together with the deep exposures to probe some of the fainter rings, including the faint G ring and the diffuse E ring. The E ring is produced by a plume emerging from Enceladus that contains both particles and copious amounts of water vapor, seen in a recent JWST observation of Saturn’s moon Enceladus.

Saturn’s atmosphere also shows surprising and unexpected detail in this JWST image. This is the first time that the atmosphere has been seen with such clarity at this particular wavelength (3.23 microns), which likely senses aerosols in the stratosphere high above the main clouds, with contributions from methane fluorescence towards the edge of Saturn’s disc. The large dark diffuse structures in the northern hemisphere do not follow the lines of latitude, so this image does not have the familiar striped appearance of Saturn that is typical of deeper layers. This patchiness is reminiscent of large-scale planetary waves in the stratospheric aerosols, perhaps similar to those that JWST saw at Jupiter. While the north-south asymmetry is consistent with known seasonal variation on Saturn, 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 the disc might be due to high-altitude methane fluorescence, emission from the H3+ ion in the ionosphere, or both; detailed spectroscopy with JWST may help decipher the ambiguity.

Provider: Space Telescope Science Institute

Image Source: https://webbtelescope.org/contents/news-releases/2023/news-2023-504

Curator: STScI, Baltimore, MD, USA

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