We Were Wrong About Uranus

Uranus. The second farthest planet from the Sun, and the long-suffering butt of the joke. Yes, let's get that out the way. This oft-forgotten orb, rarely lorded like its larger cousins Saturn and Jupiter, rolls around the solar system on its side. It has only been visited once, and even that was fleeting. The Voyager 2 spacecraft sped past on the 24th of January 1986 with just a few hours of up-close observations. For the last 40 years, this has been the foundation of what we know. No other spacecraft have even been close. But that doesn't mean new discoveries have stopped. Technological advances in telescopy and fresh takes on old Voyager 2 data have revealed a raft of remarkable new insights, some of which might rewrite the textbooks. And just in time, there's a perfectly aligned launch window opening in as little as 5 years. Whether or not we'll make a trip back to the planet is yet to be seen, but as we approach such a critical decade for revisiting Uranus, it's time to get back up to speed with this forgotten world, and unveil the latest findings. I'm Alex McColgan, and you're watching Astrum. Join me as we reconnect with our old friend Uranus, to explore its mysteries, old and new. We'll delve into Voyager's back catalogue, and show that sometimes, new discoveries don't need new data. Uranus is the 7th planet from the Sun, and since its discovery from William Herschel's back garden in 1781, only 2.9 Uranian years have passed. Each lasting 84 Earth years, the next new year is approaching in 2033. This strange world is perhaps best known for its near-horizontal tilt. Its spin axis is angled at 97.77 degrees to its orbital plane, so it essentially rolls its way around the Sun. To put that in context, Neptune's axis, at 28 degrees, is the next highest. This gives Uranus the most extreme seasons in the solar system. Each pole faces the Sun continuously for 42 years of polar day, followed by 42 years of polar night. This was pretty much all we knew about Uranus as 1985 came to a close. We guessed it might be an ice giant, and were aware of 5 moons and a ring system, but essentially, this planet was a mystery. Then, in 1986, Voyager 2 arrived, flying past on its way out of the solar system. Almost instantly, numerous discoveries were made. This enigmatic planet was revealed to be even colder than expected, challenging our fundamental ideas of how planets form and evolve. At minus 224 degrees Celsius, Uranus' atmosphere holds the record for the coldest temperature on any planet in the solar system. Voyager 2 also found a magnetic field tilted in a way we had never seen before. 11 new moons and 2 new rings. Its iconic imagery showed a calm and eerie blue-green world. But recent observations and research have built on this picture, refining, and in some cases redefining, our understanding of this sideways planet. What's more, returning to Uranus has been marked as the highest priority in NASA's planetary science programme for the next decade. With this renewed interest, let's dive into some of the most remarkable findings of recent years. Uranus is 4 times wider than Earth, with a diameter of 51,118 km, and a mass that's 14.5 times greater than our planet's. These parameters can be used to calculate its gravity, which for Uranus is a comfortable 8.7 mps2, about 89% of the gravity we experience on Earth. Grouped with Neptune as an ice giant, Uranus is believed to have a rocky silicate core, likely much smaller than Earth's, surrounded by a deep mantle of water, ammonia and methane ices. A misleading term, since its inner temperatures can soar to nearly 5,000 degrees Celsius. It's much more like a fluid ocean than ice as we might think of it. This extreme heat and the immense pressure at the base of the mantle, up to 600 gigapascals, can break down the abundant methane molecules and compress the resulting carbon atoms to form diamonds. A captivating picture, but is it right? Voyager 2 data initially said so, but new modelling published in the journal Astronomy and Astrophysics in 2025 suggests that it's perhaps not quite the whole story. The researchers Luca Morf and Ravid Hellerd of the University of Zurich took an agnostic approach, generating random models of the interior contents of Uranus and its ice giant neighbour Neptune. These were then compared to observational data and narrowed down accordingly, with one major surprise. The results show that the possible composition of Uranus is much more varied and complex than previously assumed. For example, the rock to water ratio could be as low as 0.04, making the planet almost entirely water, or as high as 3.92, making it the complete opposite, namely predominantly rock. This means that Uranus and Neptune have the potential to be rock giants instead of ice giants. What's more, if the rock-dominated option holds up, it challenges our fundamental models of solar system formation. But as the authors attest, this work is theoretical, we'll only know for sure by visiting the planet again. More on that later. Continuing out from the rocky core, the outermost layer of Uranus is comprised mostly of helium, hydrogen and 2% methane, with a cloud layer on top. Methane absorbs red light, leaving behind the distinctive blue-green hues Uranus is known for. Voyager 2, during its 1986 flyby, found Uranus cold and tranquil, with only faint clouds and a dark spot. But this veil of tranquility has been lifted thanks to telescopes including Keck, Hubble and the James Webb Space Telescope, revealing a hidden dynamism. In 2014, the W.M. Keck Observatory in Hawaii detected 8 huge storms on Uranus' northern hemisphere. Such was their intensity that, for the first time ever, amateur astronomers were able to see details in the planet's atmosphere. The largest white spot in this near-infrared image from the W.M. Keck telescope is the brightest storm ever seen on the planet at this wavelength of 2.2 microns. It's around twice as bright as anything seen before. It accounted for 30% of all the light reflected by the planet in this observation. The cloud rotating into view in the lower right also grew into a storm, spotted by amateur astronomers at visible wavelengths. Which was a lot of fun for the amateur astronomers. Of course, having the right kind of telescopes helps, no one wants to be fiddling with lenses for hours while you set things up, only for the galaxy you're looking at to still be out of focus. But if astrophotography was ever something you wanted to get into, the sponsor of today's video, Dwarf Lab, has a great, accessible option you should try. It's called the Dwarf Mini, and I've been really impressed by it. This deep space telescope has the power to image distant nebulae, but it's about the size of a paperback book, so is really convenient to carry around. Setting it up is easy, just pop it on a tripod, connect it with your phone, then tap what you want to look at. The Dwarf Mini automatically aligns itself using the stars to calibrate which way to point, and then will take up to a thousand images and stack them to give you the best possible image of your target, right then and there. Check out these images I took myself. So if you want a portable, powerful deep space telescope with no faff, check my QR code or click the link in the description below to check out the Dwarf Lab's telescope. Those who use Astrum 5 at checkout can even get 5% off their purchase. Observations by Hubble over a 20-year period found that the polar regions become noticeably more meteorologically active as the planet moves through its uniquely long seasons. Despite the study lasting two decades, Uranus was in northern spring for the entirety of this time, with the Sun starting at Equinox over the equator and moving towards the North Pole as it nears summer. The Hubble team's results, published in 2025, found bright cloud activity when the Sun was closest to the equator, with peak activity observed near the 2007 Equinox. The haze and cloud structure changed dramatically over the four observation windows, with aerosols in the atmosphere thickening at the North Pole as the planet approaches the summer solstice, which it will reach in 2030. You can see this accumulation of aerosols in these images. The North Pole changes from dark in 2002 to highly reflective in 2022, with complementary darkening of the South Pole as it moves into winter's shadow. Together, this shows that sunlight is directly altering the formation of haze and clouds in the Uranian atmosphere. The Hubble observations also identified circulation patterns that drive seasonal shifts, uncovering evidence of atmospheric gases sinking at the poles and upwelling elsewhere. The persistence of this downwelling and the changes in climate are driven by Uranus' extreme axial tilt. It's the only planet that receives more energy from the Sun at its poles than the equator, and it experiences the most radical seasonal changes in the solar system. But it's not just the Sun's light that drives this. A team at Imperial College London found that the Uranian thermosphere is also heated by the solar wind. Again, this is the only place in the solar system where this seems to happen. But as the solar wind's pressure has been dropping since 1990, Uranus has been cooling alongside it. Despite these remarkable findings, Uranus is still significantly less volatile than its cousins, Jupiter, Saturn and Neptune. They are famous for their vast storms and swirling atmospheres, and that's because these are driven by internal heat left over from the formation of these gas giants. It's the slow release of this energy that creates the turbulence they are so well known for. Which brings us to one of Uranus' great mysteries. Why is it the coldest planet in the solar system? What happened to the heat left over from its formation? Two recent studies, both published in 2025, revealed that Uranus does have its own heat, but only releases a tiny fraction of it, emitting about 15% more energy than it receives from the Sun. By comparison, its neighbour Neptune emits more than twice as much energy as it receives. This extremely low heat flux is more than just another oddity for the oddball planet, it hints at a violent past, with consequences not just for its climate and weather, but its fundamental characteristics, and even its moons. Uranus' near horizontal 97.77 degree tilt has long been thought to be a consequence of a violent historical collision, but we've only recently started to uncover the full picture. High resolution computer simulations published in the Astrophysical Journal in 2018 by Jacob Kegeris at Thuram University and his colleagues have provided a more detailed picture of how this could have happened, and the far-reaching influence it had for the planet. Their study ran more than 50 different impact scenarios in an attempt to recreate the Uranus we recognise today. The result confirmed that 3-4 billion years ago, a young Uranus was most likely dealt a glancing blow by an object 2-3 times the size of Earth, probably a protoplanet made of rock and ice. The impact would have occurred over a remarkably short period. In just a matter of hours, enough force would have been delivered to reorient Uranus' axis, knocking it to its side, and it set in motion a series of events that created the planet we see today. The simulations show that most of the protoplanet was deposited in Uranus, creating a hot, high entropy shell in the icy interior. Highly disordered, high entropy materials don't conduct heat well, so this layer acts like an insulation, trapping heat deep inside the planet and helping to explain the low heat flux and extreme coldness we see on Uranus today. This unique interior structure may also help explain Uranus' profoundly weird magnetosphere. Usually, these invisible magnetic shields originate from the geometric centre of a planet, its core, but that's not the case here. Voyager 2's original flyby discovered that its magnetic field is tilted by almost 59 degrees from its rotational axis, and offset from the planet's centre by a third of the planet's radius. This magnetic misalignment creates an asymmetric magnetosphere, with a magnetotail that corkscrews into space for millions of kilometres. When Voyager 2 flew past, the magnetosphere actually appeared to be much smaller than thought, and this has baffled scientists for decades. Recent re-analysis of the original data, led by Jamie Jaczynski at NASA JPL and published in Nature Astronomy in 2024, finally provided an answer. When Voyager arrived, it was in the midst of some violent space weather that compressed the planet's magnetic field, something NASA couldn't have planned even if they tried. The new study instead suggests that the planet's magnetosphere is actually even larger and more active and variable than initially thought. The reason for such a strange magnetosphere isn't fully understood, but it could be that fields don't originate from the planet's core at all, rather they come from the convecting mantle influenced by the deposits left by that ancient collision billions of years ago. For us at least, this has had one serious upside. The off-kilter magnetosphere leads to stunning, sprawling auroras that do not align with the poles like on Earth, Jupiter or Saturn. These phenomena have been imaged by Hubble in both the visible and ultraviolet parts of the spectrum, and by studying a decade of these images, scientists recently calculated Uranus' rate of rotation with 1,000 times greater accuracy than before. Their technique revealed the planet completes a full rotation in 17 hours, 14 minutes and 52 seconds, 28 seconds longer than the estimate obtained by Voyager 2. And I simply couldn't miss out including this stunning representation. It shows infrared auroras, which, after 30 years of study, were finally detected on Uranus in 2023 using the Keck 2 telescope. But the consequences of Uranus' violent past haven't ended yet. At the time of impact, its largest moons hadn't formed. Instead, the planet sat amid a disk of stuff, for lack of a better word, with the impact jettisoning further rock and ice into orbit around the planet. As this started to clump together to form the five largest moons, Uranus' new axial plane acted like a gravitational tidal wave, pushing them to the same tilt. As of now, Uranus has 29 confirmed moons, two more than when I last made a video about the planet. Moon 28 is currently called by the rather catchy title S2023U1, and was discovered in 2023 by Scott Shepard using the Las Campanas Observatory in Chile. The most recent addition, its 29th moon, was made in February 2025 by using the James Webb Space Telescope's NIRCAM. Designated S2025U1, it is yet to be officially named. Let me know if you have any great suggestions for names in the comments. This startling array of moons is divided into three categories, 14 inner moons, 5 major moons, and 10 irregular satellites. Romantically, they are named after characters from English literature. The major moons, Miranda, Ariel, Umbriel, Titania, and Oberon, feature diverse compositions dominated by water ice and rocky material. Studies published in 2025, it was a very busy year for Uranus scientists, hint at possible differentiated interiors, with liquid oceans sandwiched between rocky cores and icy mantles, which of course raises the tantalising question of whether they are habitable for life. But again, only an actual visit could tell us that. Like its immediate neighbours, Saturn, Jupiter and Neptune, Uranus has a ring system. They are aligned with its tilted spin axis, so during Voyager 2's approach 40 years ago, they appeared almost like a bullseye. The rings are very young by solar system standards, thought to be a mere 600 million years old, and they are believed to have been formed by the breakup of a small moon colliding with a meteorite or a comet. Their most remarkable feature is how dark they are. With an albedo of less than 2%, they are made of the darkest material in the solar system. What exactly that is, is of yet unknown, but scientists think it could be particles of water ice mixed with organics or methane ice singed black. Against Uranus' bright exterior, the rings are really difficult to discern, so much so that they were discovered by accident in 1977 thanks to a star occultation, an event in which Uranus moved in front of a star, and the subsequent dimming confirmed the presence of the rings. Thirteen rings have now been imaged thanks to Voyager 2, as well as the Advanced Telescopy of Hubble, Keck 2 and James Webb. They range from a few kilometres wide to roughly 100 kilometres wide, and it's unclear why some of the rings are kept so narrow. Shepard moons may help maintain the structure of some of them, but for most, the mechanics remain obscure. Excitingly, a rare stellar occultation happened again in April 2025, with Uranus passing in front of a star about 400 light years from Earth. This led to a coordinated effort to observe Uranus like nothing done before. Led by planetary scientists at NASA Langley, an international team of over 30 astronomers using 18 observatories simultaneously trained their attention on Uranus for about an hour. It was the largest campaign ever organised, and the largest simultaneous observation of Uranus since Voyager 2's 1986 flyby. The nature of an occultation is perfect for studying Uranus' atmosphere and rings. Atmospheric findings are yet to be released, but the precision of the ring data, specifically the timings of each occultation, have allowed scientists to determine where Uranus is in its orbit, updating its position by around 400km. This is critical information for sending a physical mission, but I'll talk more on that later. This unprecedented coordination is just the beginning. Over the next decade, Uranus is set to pass between Earth and the galactic centre of the Milky Way, prime opportunity to carry out further occultation studies, with the best ever conditions lined up for 2031. The last few years have been a flurry of publications and activity, looking at you 2025, focused on the strange 7th blue-green sideways planet, revealing it to be a dynamic world with a storied past and enigmatic features. So much has been learned since William Herschel stood in his back garden looking through a homemade telescope, and that's despite Uranus and its neighbour Neptune being the least visited planets in the solar system, even more discovery lies ahead still. The 2023 Planetary Science Decadal Survey has made a Uranus orbiter and probe mission NASA's top planetary priority, and the Chinese National Space Administration have also proposed a mission to the planet with Tianwen-4. With the possibility of another visit on the horizon, scientists will need to look sharp as we are approaching a critical window. 2031 and 2032 are optimal launch opportunities. Thanks to planetary alignments, a future spacecraft could get a gravity assist from Jupiter, shortening the journey by several years. Mission objectives are set to include mapping the planet's gravity and magnetic fields over time, studying the weather systems and atmospheric composition, characterising rings and investigating the potential habitability of its moons. So stay tuned. The next chapter of Uranus exploration is being written as we speak. Have you ever wanted to ask us a question? Our favourite section of the newsletter is dedicated entirely to questions and answers. Just sign up down below and reply to one of our auditions with anything you've been wondering about. It can be about space, science, or even how we make our videos. We love hearing from readers and featuring your questions in future issues. It's a simple way to join the conversation and be part of the Astrum community. So if curiosity ever strikes you, make sure you're on the list and ready to send in your first question.