Saturn through Hubble, Webb and ground-based telescopes
Telescopes are now the only eyes on Saturn. Since Cassini ended in 2017, the Hubble Space Telescope has imaged the planet every year through its OPAL program, the James Webb Space Telescope photographed it in infrared in June 2023 and traced a giant water plume from Enceladus, and ground-based telescopes keep finding moons, including 128 announced in March 2025. Their long, regular records complement the close-up but brief views of spacecraft.
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Why telescopes still matter
A spacecraft gives detail; a telescope gives time. Saturn's year lasts 29.46 Earth years, so its seasons unfold over decades, longer than any mission. Cassini covered about half a Saturn year, from northern winter to the northern summer solstice of May 2017. Telescopes extend that record backward and forward, and they can watch the whole planet at once.
Hubble: three decades of Saturn weather
Hubble's early views caught the Great White Spot of 1990, a storm that erupted in September and spread around the equator. Such storms appear roughly once every Saturn year, near northern summer: 1876, 1903, 1933, 1960 and 1990. A storm of similar scale arrived early, in December 2010, and Cassini watched it close up (see Saturn's storms).
Hubble also followed the ring-plane crossings of 1995–1996, when the rings turned edge-on and faint moons became easier to spot, and recorded Saturn's ultraviolet auroras, including joint campaigns with Cassini that linked them to the solar wind.
Since 2018 the Outer Planet Atmospheres Legacy program, OPAL, has imaged Saturn each year near opposition with the same filters, so that changes in cloud bands, colors and the north polar hexagon can be compared year to year. These images showed the color of the northern hemisphere shifting with the seasons and the return of ring spokes in the early 2020s as the rings approached the 2025 equinox, a test of the theory that sunlight angle controls them.
Webb: Saturn in infrared
The James Webb Space Telescope observes in infrared, where Saturn behaves very differently. In its image of 25 June 2023, taken with NIRCam at a wavelength of 3.23 microns, methane in the atmosphere absorbs most of the sunlight, so the planet appears dark while the icy rings shine brilliantly. High-altitude haze stands out, and three moons, Dione, Enceladus and Tethys, are visible nearby. The image was a short test of how well Webb could detect faint moons and ring structures next to a bright planet.
Webb's spectrometers also look at chemistry. In 2023, a team led by Geronimo Villanueva reported that a water vapor plume from Enceladus extended more than 9,600 km, about 20 times the moon's diameter, and that the water spreads into a torus along its orbit, feeding Saturn's E ring. Webb observed Titan together with the Keck Observatory in November 2022, tracking clouds in its northern hemisphere.
| Telescope | Strength | Notable Saturn results |
|---|---|---|
| Hubble | Visible and ultraviolet, long record | Great White Spot 1990, auroras, OPAL weather maps, spokes |
| Webb (JWST) | Infrared sensitivity | Infrared portrait 2023, Enceladus water torus, Titan clouds |
| Spitzer (retired 2020) | Infrared, wide field | Discovery of the giant Phoebe ring, 2009 |
| Large ground telescopes | Size, adaptive optics, long campaigns | New moons, ring rain, storms |
Ground-based telescopes
New moons
The moon count has grown mostly from the ground. Using the Canada-France-Hawaii Telescope on Maunakea, a team led by Edward Ashton stacked many exposures taken while tracking the expected motion of faint objects, revealing tiny, distant irregular moons. The 62 moons announced in 2023 and 128 more in March 2025 brought the total to 274.
Ring rain and the upper atmosphere
In 2011, observations with the Keck telescope in Hawaii mapped infrared emission from H3+ ions in Saturn's upper atmosphere and found dark bands matching the rings' magnetic connections: charged water from the rings falling into the planet. The result, published in 2013, was later confirmed directly by Cassini's Grand Finale (ring rain).
Occultations
When Saturn or its rings pass in front of a star, the starlight's flicker maps the rings and probes the atmosphere. The occultation of the star 28 Sagittarii in July 1989 was observed from many observatories and remains a reference for ring structure.
Amateurs
Amateur astronomers with modest telescopes and video cameras regularly catch new storms first, as with the December 2010 storm. Their images feed professional monitoring. The page on photographing Saturn explains the techniques.
The Phoebe ring
In 2009, NASA's Spitzer Space Telescope detected the largest ring in the Solar System: a vast, faint torus of dust tilted by about 27 degrees, extending millions of kilometers from Saturn along the orbit of the moon Phoebe. It is invisible in ordinary light and was found only through its infrared glow. See the Phoebe ring.
For how this work fits into four centuries of observation, from Galileo's first sighting onward, see the history of Saturn observation.
FAQ
Has the James Webb telescope photographed Saturn?
Yes. Webb captured Saturn on 25 June 2023 with its NIRCam camera at 3.23 microns. The planet appears dark because methane absorbs that wavelength, while the rings and three moons shine brightly.
Why does Saturn look dark in the Webb image?
At 3.23 microns, methane gas in Saturn's atmosphere absorbs most incoming sunlight. The water-ice rings reflect strongly at that wavelength, so they look much brighter than the planet.
Does Hubble still observe Saturn?
Yes. Through the OPAL program, Hubble has imaged Saturn every year since 2018 to track changes in its atmosphere, colors, storms and ring spokes.
Can telescopes on Earth discover new moons of Saturn?
They do. The Canada-France-Hawaii Telescope was used to find 62 moons announced in 2023 and 128 announced in 2025, all small irregular moons a few kilometers across.
Sources
- NASA Science: Hubble Space Telescope
- Webb Space Telescope (STScI)
- Villanueva, G. L. et al., "JWST molecular mapping and characterization of Enceladus' water plume feeding its torus", Nature Astronomy 7, 2023
- O'Donoghue, J. et al., "The domination of Saturn's low-latitude ionosphere by ring 'rain'", Nature 496, 2013
- Verbiscer, A. J., Skrutskie, M. F., Hamilton, D. P., "Saturn's largest ring", Nature 461, 2009