Chapter 1: What new discoveries have been made 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.
Chapter 2: Why is Uranus considered a forgotten planet in our solar system?
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 five 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 seventh 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 five 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 program 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 m2, 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 5000°C. It's much more like a fluid ocean than ice as we might think of it.
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Chapter 3: What insights have recent technological advances provided about Uranus?
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 tranquillity has been lifted thanks to telescopes including Keck, Hubble, and the James Webb Space Telescope, revealing a hidden dynamism. In 2014, the WM Keck Observatory in Hawaii detected eight 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 WM 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 it's really convenient to carry around. Setting it up is easy.
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Chapter 4: How does Uranus' unique tilt affect its seasons?
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's 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 axle 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 hint at possible differentiated interiors, with liquid oceans sandwiched between rocky cores and icy mantles, which of course raises the tantalizing 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're 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.
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Chapter 5: What did Voyager 2 reveal about Uranus during its flyby?
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