Eleven of Uranus’ thirteen rings are spectacularly visible in images taken by the James Webb Telescope in February 2023 during just a 12-minute infrared exposure. We can therefore expect even more beautiful images in the future, especially since we can already see several of the 27 known moons of Uranus with the JWST.
Uranus’ rings are so faint in the visible that it took astronomers and computer scientists James L. Elliot, Edward W. Dunham, and Jessica Mink until 1977 to make their discovery from Earth. Then it will be necessary to await the visit of the Voyager 2 probe in 1986, so that two rings are discovered in addition to the nine previous ones. Two more rings were discovered by the Hubble telescope from 2003 to 2005.
We are therefore impressed by the new infrared images from the James Webb Telescope (JWST), which are particularly sharp. Unfortunately André Brahic is no longer there to comment on them with us, he is the great specialist on the planetary rings of the solar system. We had already missed him when the JWST also revealed images of Neptune’s rings in 2022, of which he was one of the co-discoverers.
A presentation of Uranus and its many singularities. For a fairly accurate French translation, click the white rectangle at the bottom right. Then the English subtitles should appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose French. ©National Geographic
A polar cap at the equator
NASA and ESA just showed us these images of Uranus. Keep in mind that the planet is special because, as explained in the video above, its axis of rotation is almost parallel to its orbital plane, implying much more extreme seasons than on Earth, with a year lasting 88 Earth years and a kind of polar cap that’s on the equator, so to speak. Also remember that Neptune, like Uranus, is an ice giant and not a gas giant like Jupiter and Saturn.
As explained in the press release on the images taken by James-Webb’s near-infrared (NIRCam) camera with its two filters at 1.4 and 3.0 microns, yielding false-color photos shown here in blue and orange, it is End of Spring the North Pole that the JWST allows us to look at. We’ll have to wait until 2028 to see summer in the northern hemisphere. When Voyager 2 visited Uranus, it was summer at the South Pole.
rings, clouds and moons
As the Voyager 2 probe approached Uranus, it didn’t have the ability to see in the infrared like the JWST, so we’re now seeing never-before-seen details of the ice giant’s atmosphere, like the two clouds, one of which is very bright, on the left side of the image of Uranus and the other, which is less, at the edge of the northern polar cap of Uranus. However, we had seen such clouds before in the near-infrared, particularly thanks to adaptive optics techniques at the Keck Observatory in Hawaii, which we know are typical of Uranus.
We also clearly see a type of polar cap specific to Uranus, which we know appears mysteriously as the pole enters directly into sunlight in summer and disappears in fall. The JWST observations should help us understand the mechanism behind its formation.