We’ve just been given a spectacular new perspective on what is perhaps the strangest ball in the solar system.
The James Webb Space Telescope turned its golden, infrared gaze on the Sun’s enigmatic seventh world, Uranus – and the image it sent back revealed the turquoise planet in sparkling glory. Moons, rings and all.
Each planet and dwarf planet in the solar system has its own set of quirks and idiosyncrasies that make it special, but Uranus is truly special. The icy, frozen world, at first glance, seems fairly mundane, but the closer you look, the weirder – and more beautiful – it becomes.
But you have to look beyond the colors our own eyes can detect, in which Uranus appears to be a relatively featureless pale blue orb. Using thermal imaging, for example, including radio and infrared wavelengths, scientists have been able to measure the physical properties of the faint icy rings of Uranus.
JWST is the most powerful space telescope ever launched, and it sees the Universe exclusively in infrared and near infrared. This makes it perfect for capturing the stretched glow of light that has spilled out billions of years into our past.
Fortunately, this infrared sensitivity can do more than look deep into space to observe the dawn of the Universe; it’s equally useful for looking at things closer to home to help understand the mysteries of our own solar system. Since infrared wavelengths can reveal a lot about how Uranus works, JWST was reserved for a closer look.
Although the allotted time was only 12 minutes, the space telescope could still resolve never-before-seen details.
One thing you’ll quickly notice about Uranus is its unusual sideways rotation relative to its orbital plane. This means that its polar seasons are very different from those of other planets. During its 84-year orbit, the poles of Uranus will receive the full brunt of glare from the Sun in summer, but total darkness in winter.
When Voyager 2 flew by Uranus in 1986, it was summer at the South Pole; now it’s late spring at the north pole, with summer set to hit in 2028.
This means the JWST was able to image a feature unique to Uranus: polar brightening as the planet moves through the full light of the summer Sun. The cause of this bright polar cap is unknown, but scientists believed that the unprecedented resolution provided by the JWST could provide new information.
And they weren’t wrong. The data reveals a subtle but unequivocal region of increased brightening in the center of the polar cap.
We still don’t know why, but scientists will be able to take this information into account when studying the phenomenon in detail.
Other bright features visible in the image are clouds, linked to storm activity in the icy giant’s predominantly hydrogen and helium atmosphere.
Although hardly as famous as Saturn’s amazing set of rings, Uranus itself has just over a dozen humble circles. The JWST has photographed 11 of the 13 known rings surrounding the planet, including the two faint and dusty inner rings that are so dark they weren’t discovered until Voyager 2 passed by in 1986.
Scientists hope that future JWST observations can also capture the two faint outer rings, beyond the main cluster.
Finally, the telescope captured many – but not all – of Uranus’s 27 known moons. Some are too weak to be seen. But these moons have very different orbits. The six moons seen in the image above all share their orbital plane with the equatorial plane of Uranus, as do the smaller inner moons. But Uranus also has a collection of much more distant, irregular moons that have inclined, elliptical orbits, similar to those of Jupiter’s irregular moons.
Studying the details of these moons can be helpful in understanding how Uranus came to be, a tricky question that eludes simple answers.
Other JWST observations of Uranus are underway or planned for the future. Hopefully, they can help scientists make a compelling case for sending a dedicated probe into this intriguing world.
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