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Starts With A Bang

Uranus is “boring” again, JWST shows. Here’s why.

Voyager 2 flew past Uranus in 1986, finding a bland, featureless world. Now, in 2023, JWST’s sights are similar. There’s a reason for that.
Uranus 1986 Voyager 2 2023 JWST
As seen up-close in 1986 by Voyager 2 (left) and from far away in 2023 by JWST (right), Uranus has returned to being a relatively featureless, monochromatic world. However, it wasn't like this at all near its 2007 equinox, showcasing the need for advanced imaging during the next Uranian equinox in 2049.
Credit: NASA/Voyager 2 (L), NASA, ESA, CSA, STScI, Acknowledgement: J. DePasquale (STScI) (R), annotation: E. Siegel
Key Takeaways
  • Uranus, our Solar System’s 7th planet, was discovered in 1781: more than 240 years ago.
  • With an 84-year orbital period, we’ve experienced nearly three full Uranian revolutions, but didn’t get our first close-up glimpse until Voyager 2 flew past in 1986.
  • JWST just released its first views of Uranus, finding a world very similar to what we saw nearly 40 years prior. But it won’t always be this way, and science knows why.

Uranus, discovered in 1781, has only been visited once: via spacecraft.

Voyager 2 took this image as it approached the planet Uranus on Jan. 14, 1986. The planet’s hazy bluish color is due to the methane in its atmosphere, which absorbs red wavelengths of light. This image, however, does not represent how Uranus appears at most times in its orbit around the Sun; only at or near Uranian solstice.
Credit: NASA/JPL-Caltech

In 1986, NASA’s Voyager 2 flew past Uranus.

raw image uranus rings voyager 2
Taken only 3.5 hours after Voyager 2’s closest approach of Uranus, this wide-angle exposure shows the delicate, see-through rings of Uranus, where this image frame “only” spans about 10,000 kilometers. The short streaks are background stars. Uranus’s rings are made of ~micron-sized particles, are very dark, and are primarily interior to Uranus’s 5 major moons.
Credit: NASA/Voyager 2

Its moons and glorious, inner rings were revealed in great detail.

Uranus and its five major moons are depicted here in this montage of images acquired by the Voyager 2 mission in 1986. The five moons, from largest to smallest, are Ariel, Miranda, Titania, Oberon, and Umbriel. Puck, the 6th largest moon, is interior to all of them, and appears in the first JWST image of Uranus alongside these five.
(Credit: NASA/JPL)

But Uranus itself appeared disappointingly monochrome and featureless.

uranus true false color voyager 2
True color (left) & false color (right) views of Uranus as depicted by NASA’s Voyager 2 spacecraft, at a range of 5.7 million miles. While Uranus might appear to be a monochrome, featureless world, this is largely due to its orientation and orbital properties at the time we flew past it in 1986. By stacking many varied images together of this world, a reanalysis was able to reveal features that were originally unseen.
Credit: NASA/Voyager 2

Fortunately, this boring, bland side of Uranus is temporary.

planets solar system axial tilt
Although all of the worlds in the Solar System rotate about their axis as they orbit the Sun, most worlds orbit within 25 degrees (or less) of the Sun’s rotational plane. Only Uranus is different, rotating on its side as it revolves around the Sun, only ~7-8 degrees away from a perfectly perpendicular orientation.
Credit: cmglee/Wikimedia Commons, NASA and Solar System Scope

Unlike all other planets, Uranus orbits the Sun while rotating sideways: like a barrel.

uranus neptune 2mass
As observed in 1998 by the infrared 2-Micron All Sky Survey (2MASS), Uranus and Neptune appear blue and have their own lunar systems orbiting them. Uranus was discovered by pure chance in 1781, with its moons nearly all orbiting in a coplanar fashion, aligned with its rings. This photo of Uranus was taken in ~1998, approximately mid-way between solstice and equinox.
Credit: Two Micron All Sky Survey (2MASS), UMASS/IPAC/Caltech, NASA and NSF, Acknowledgement: B. Nelson (IPAC)

Near solstice, one pole faces the Sun, where that hemisphere receives constant heat.

uranus solstice rings inner clouds jwst
This annotated view of a near-solstice Uranus comes courtesy of JWST, which showcases a bright cloud on the left of the planet, the polar cloud cap toward the right, and the nearly face-on rings of Uranus. Taken in 2023, just ~5 years before solstice, the northern pole of Uranus is 16 years in to receiving 42 continuous years of direct sunlight.
Credit: NASA, ESA, CSA, STScI, Acknowledgement: J. DePasquale (STScI)

Its rings appear maximally illuminated as observed from an inner planet.

The final two (outermost) rings of Uranus, as discovered by Hubble, along with atmospheric features that appear in the infrared. We discovered so much structure in the inner rings of Uranus from the Voyager 2 fly-by, but a long-term orbiter could show us even more than any ground-based or near-Earth space-based telescope can reveal.
Credit: NASA, ESA, and M. Showalter (SETI Institute)

But near equinox, it receives planet-wide, uneven day-night heating.

Although this is a modern, infrared view of our Solar System’s 7th planet, it was only discovered in 1781 through the serendipitous observations of William Herschel. We can see bands, clouds, aurorae, storms, and more when Uranus is near equinox, but it appears largely featureless when viewed near solstice.
Credit: ESO

With an 84-year elliptical orbit, Uranus last experienced equinox in 2007.

Infrared images of Uranus (1.6 and 2.2 microns) obtained on Aug. 6, 2014, with adaptive optics on the 10-meter Keck telescope. The white spot is an extremely large storm that was brighter than any feature ever recorded on the planet in the 2.2-micron band. The cloud rotating into view at the lower-right limb grew into a storm that was so large, it was visible even to amateur astronomers at visible wavelengths. These features were not present in 1986, when Voyager 2 flew by Uranus.
Credit: Imke de Pater, UC Berkeley & Keck Observatory

Near equinox, Uranus appears non-uniform and feature-rich.

uranus dark spot 2006 Hubble
This Hubble image shows Uranus with a dark spot clearly visible on the eastern side. This dark spot is a vortex measuring 1,100 miles by 1,900 miles — large enough to engulf two-thirds of the United States — and was caused by churning winds in the planet’s atmosphere. The “left” side represents the Southern Uranian Hemisphere while the right is the Northern Hemisphere, and these photos were taken 1 year before Uranian equinox: in 2006.
Credit: NASA, ESA, L. Sromovsky and P. Fry (University of Wisconsin), H. Hammel (Space Science Institute), and K. Rages (SETI Institute)

It experiences banding, color differentials, and even storms and aurorae.

Keck adaptive optics 2004 two hemispheres uranus
These two images show Uranus, on the same day, as imaged ~8.6 hours apart: showcasing both hemispheres of Uranus. The brighter side has experienced solstice more recently, while the darker side is getting more and more exposed as 2007’s equinox approaches in this 2004 image. Features like bands, storms, and even aurorae can be seen on Uranus.
Credit: Lawrence Sromovsky, University of Wisconsin-Madison/W.W. Keck Observatory

Its rings also appear thin and tilted, as they’re nearly edge-on.

infrared views uranus rings
This series of images of Uranus show our Solar System’s 7th planet as it approaches its 2007 equinox. From our perspective, its rings become more edge-on, but the storm activity in the southern and northern hemispheres intensifies. Uranus is more uniform-appearing near solstice and more active-appearing near equinox.
Credit: Keck Observatory

Now, however, we’re nearing Uranian solstice once again.

uranus hubble 2018
This 2018 image of Uranus from Hubble shows how the planet changes as it progresses from equinox toward solstice. The bright northern pole experiences a cloud cap, while the clouds and banding features across the rest of the world are decreasing. Uranus will next reach solstice in 2028.
Credit: NASA, ESA, and A. Simon (NASA Goddard Space Flight Center), and M. Wong and A. Hsu (University of California, Berkeley)

JWST’s first Uranus image looks familiar.

Uranus first wide-field view JWST
This wide-field view of Uranus, taken with JWST, reveals the planet, cloud-like features on it, the inner rings that surround it, as well as the 6 brightest (annotated) of Uranus’s 27 known moons. Background objects, like galaxies, are also visible owing to JWST’s incredible capabilities.
Credit: NASA, CSA, ESA, STScI; Processing: J. DePasquale (STScI)

Blue and featureless, it’s reminiscent of Voyager 2’s 1986-era views.

Uranus with rings, Ariel, Miranda, and Puck
Shown here with its inner ring system, as well as three of its six largest moons, this JWST view of Uranus reveals its northern polar cloud cap along with a bright, reflective cloud feature on the planet itself. The rest of Uranus is featureless and monochrome: a typical “solstice” view of Uranus.
Credit: NASA, CSA, ESA, STScI; Processing: J. DePasquale (STScI); Crop: E. Siegel

Uranian solstice arrives in 2028.

seasons of uranus equinox solstice dates
When Voyager 2 flew by Uranus in 1986, the planet was near solstice, with its southern hemisphere facing the Sun and its northern hemisphere facing away. In 2007, Uranus achieved equinox, and now heads toward its next 2028 solstice. It won’t reach equinox again until 2049, when JWST will likely be out of fuel and defunct.
Credit: M. Showalter & M. Gordon, SETI Institute; modification by E. Siegel

We now see Uranus’s opposite pole, as its other side faces a decades-long winter.

uranus equinox features keck
As Uranus migrates through its orbit, its poles alternately experience 42 years of sunlight and 42 years of darkness. As the northern hemisphere became more illuminated than the southern in 2007, the bright southern hemisphere’s bands waned while the northern hemisphere’s waxed. Closer to solstice, the banded appearance disappears entirely, giving way to a monochrome perspective.
Credit: Keck Observatories/SSEC

JWST won’t survive until the next Uranian equinox, however.

JWST Jupiter scale
This animation showcases JWST’s unique near-infrared views of Jupiter. In addition to the bands, the great red spot, and the “atmospheric haze” visible at the day/night boundary of Jupiter, a number of moon, ring, and auroral features are seen and labeled. A single NIRCam or MIRI frame is just barely large enough to hold all of Jupiter’s disk within it, enabling spectacular views of this world with JWST. With an expected lifetime to last until the mid-2040s, JWST will observe multiple Jovian solstices and equinoxes, but won’t last until Uranus reaches its equinox phase.
Credit: NASA, ESA, CSA, Jupiter ERS Team; Processing: R. Hueso (UPV/EHU) & J. Schmidt

The dream is to launch an in situ mission, fully uncovering Uranus’s changing properties.

Uranus orbiter and probe mission 2020 decadal
Although the ideal launch window for an orbiter-and-probe mission to Uranus occurs between 2030 and 2034, our expected spaceflight capabilities in the 2030s should allow this mission to arrive in or near Uranian equinox, giving us a never-before seen, close-up view of our Solar System’s 7th planet.
Credit: NAS 2020 decadal survey

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.