Why is Uranus on its Side?

It’s impossible to do an article about Uranus without opening up the back door to a spit storm of potty humour. I get it, there’s something just hilarious about talking about your, mine and everyone’s anus. And even if you use the more sanitized and sterile term urine-us, it’s still pretty dirty, in an unwashed New York stairwell kind of way. You’re in us? No.

This is a no-win solution. It’s a Kobayashi Maru scenario here. We’re all doomed.

Can we call a truce? I dare you commentators, to keep the YouTube comments as pure and clean as driven snow, so we can focus on the super interesting science. Think of the children.

Let’s set the stage, I’m going to let planetary astronomer Kevin Grazier give you the proper pronunciation to clear our minds and let us move forward with grace and civility.


Kevin Grazier:
Strictly speaking, it’s pronounced Youranous, is the  pronunciation.


As you probably know, Uranus… I mean Ouranus. No, I can’t do it, my brainwashing is too far along. Save yourselves!. Anyway, Uranus is the 7th planet from the Sun, and the 3rd largest planet in the Solar System. Jupiter and Saturn get all the spacecraft and Hubble space telescopes, but Uranus is an incredibly worthwhile target to visit.

Diameter comparison of Uranus and Earth. Approximate scale is 90 km/px. Credit: NASA
Diameter comparison of Uranus and Earth. Approximate scale is 90 km/px. Credit: NASA

It’s almost exactly 4 times larger than Earth and has its own set of strange dusty rings – perhaps left over from a shattered moon. It has at least 27 moons, that we know of, and many more interesting features that would fascinate astronomers, if we had a spacecraft there, which we don’t. Which is ridiculous. We’ve only made one close flyby of Uranus by Voyager II back in 1986.

We’ve seen Pluto up close, but there are no plans to visit Uranus? Madness.

Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.
Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

Anyway, perhaps one of the strangest aspects of Uranus is its tilt. The planet is flipped over on its side, like a Weeble, that wouldn’t unwobble.

Actually, all the planets in the Solar System have some level of axial tilt. The Earth is tilted 23.5 degrees away from the Sun’s equator. Mars is 25 degrees, and even Mercury is 2.1 degrees tilted. These tilts are everywhere.

But Uranus is 97.8 degrees. That’s just 0.2 degrees shy of a 90s boy band.

You might be wondering, why have it be more than 90 degrees. High school geometry tells me that 97.8 degrees is the same as 82.2 degrees. And that’s true. But astronomers define the angle as greater than 90 degrees when you take its direction of rotation into account. When you describe it as turning in the same direction as the rest of the planets in the Solar System, then you have to measure it this way.

What could have done that to Uranus, how could it have happened?

The fact that Uranus is flipped over on its side tells us that the calm clockwork motion of the Solar System hasn’t always been this way. Shortly after the formation of the Sun and planets, our neighborhood was a violent place.

The early planets smashed into each other, pushed one another into new orbits. Some planets could have been spun out of the Solar System entirely, while others might have been driven into the Sun. Our own Moon was likely formed when a Mars-sized object crashed into the Earth. Other moons might have been captured from three body interactions between worlds. It was mayhem.

The Solar System that you see today contains the survivors. Everything that wasn’t delivered a death blow.

And something really tried to deliver a death blow to Uranus, very early after it formed. We know this because the moons of Uranus orbit at the same tilt as the planet’s axis. This means that something smashed into Uranus while it was still surrounded by the disk of gas and dust that its moons formed from.

When the massive collision happened, the planet flipped over, wrenching this disk with it. The moons formed within this new configuration.

Astronomers think it was more complicated than that, however. If it was a single, massive collision, models suggest the planet would just flip over entirely, and end up rotating backwards from the other planets in the Solar System.

It’s more likely that another collision or even a series of collisions put the brakes on Uranus’ end over end roll, putting it into its current configuration. It boggles the mind to think about what must have happened.

Uranus' tilt drastically affects the amount of sunlight the hemispheres receive during its orbit. Credit: NASA, ESA, and A. Feild (STScI)
Uranus’ tilt drastically affects the amount of sunlight the hemispheres receive during its orbit. Credit: NASA, ESA, and A. Feild (STScI)

Having such a huge axial tilt makes a big different to Uranus. As it travels around the Sun in its 84-year orbit, the planet still has its poles pointed at fixed locations in space. This means that it spends 42 years with its northern hemisphere roughly pointed towards the Sun, and 42 years with its southern hemisphere in sunlight.

If you could stand on the north pole of Uranus, the Sun would be directly overhead in the middle of summer, and then it would make bigger and bigger circles until it dipped below the horizon a few decades later. Then you wouldn’t see it for a few decades until it finally reappeared again. It would be very very strange.

Of course, it’s a gas planet, so you can’t stand on it. If you could stand on it, we’d all be marveling at your ability to stand on planets.

Here we are in our calm, ordered Solar System, everything’s business as usual. But if you look around, you realize it’s pretty amazing that our planet is even here. Poor sideways Uranus is a testament to our good luck.

Book Review: Hollyweird Science

Gravity movie poster

Do you remember science classes from way back when? All those laws and rules made it seem like everything was logical and well behaved. Then perhaps with television and movies being a big part of your life you began to wonder whether what you saw was real and unreal. Those things on the big and small screens didn’t seem nearly as well behaved. For instance, can people hear sounds in space? Or, can travelers quickly and easily go from one star to another? If you want to get yourself back on solid footing, get a hold of the book “Hollyweird Science – From Quantum Quirks to the Multiverse” by Kevin Grazier and Stephen Cass. With it, you can sift through a lot of tropes and conceits and glean some wonderful insights of both modern science and modern cinema.

Yes, tropes and conceits are terms from the world of cinema and not of physics. Think of these terms as ‘untruths’ for entertainment that writers use to capture and hold the attention of the audience. As this book describes, writers conjure up these exigencies to meet their demands. Their main demand is to prepare a story that fits into a very limited timeframe and into a very limited budget.

HollyweirdAnd much of the first part of this book takes the reader on a journey of past and present cinema that involves detailed science. This part of the book substantiates the claim that science in the Hollywood world of cinema is weird, whether it is Superman’s kryptonite, Star Trek’s dilithium crystals or Godzilla’s shear bulk. So how does this book go about proving that the science is weird?

Ah, this is the part that you may either love or hate. The authors include science boxes at regular intervals throughout. These science boxes have the equations you may remember from your early science classes. And the equations include numbers or ratios that show how a trope or conceit is particularly untrue. That is, the authors return to all those laws and rules of science, such as the law of gravity, the formula for acceleration, and the standard chemical composition of ecosystems.

Nevertheless, most of these weird issues are ones that the audience has already accepted and even a science box won’t affect the shear enjoyment. For example, think of Torch, a human that can instantly become a flame even though there’s no fuel. While the authors do raise a general lament on the failure of cinema to faithfully follow science, they do provide some rationalization that the untruth or trope was necessary, whether to fit a timeframe or a budget. Perhaps most promising from this section of the book is that the authors indicate that the typical audience member has become much smarter. In consequence, writers put a lot more reality into their science and even the depiction of alien worlds.

Who knew that learning physics could be so much fun?

Overall, the first third of the book is a fairly light, simple read with not so many science boxes. At about a third of the way in, however, the book transitions from being a discussion of cinema entertainment, with particular attention to its science, and becomes a discussion of science with reference to cinema. Here the science boxes are more detailed and numerous. They assess the possibility of using material from the Earth to kick-start a failing Sun, as done in a movie. Or, the likelihood of the Earth’s Moon being kicked out of the solar system, also done. And there’s much detail on the holy grail of science cinema, the faster than light transportation, as happens in most science fiction cinema.

Reading through this part of the book may bring you right back to your science classes of yore and their laws and rules. That is, it will if your science classes included quantum mechanics, parallel universes and wormholes. Here in the book things get really weird as today’s science has yet to faithfully prescribe the laws. Thus, the authors introduce a whole field of science, add current investigations and then associate the science with somewhat related relevant films. Perhaps, when the science gets this challenging, then it’s a good thing that entertaining cinema can come along and at least introduce the ideas to the general public.

With all the attention that the authors give to the science in this book, the reader will quickly appreciate that the book is not just a simple list of cinema bloopers. Rather, the book’s details provide enough depth of knowledge to allow the reader to hold their own at lunch time conversations when the topic swings around to the science in the latest show or movie. Perhaps it may induce the reader to do a bit more exploring and learning, especially as many current films feature a website that defines the science, the tropes and the conceits. However, cinema is for entertainment and the authors must realize the same holds for their book. So as much as this book has lots of hard science, the authors still keep the book entertaining.

And entertainment is mostly what we want, whether from cinema or books. So even if explosions in space come with a loud bang on the sound track or people fly without space suits up and around the Moon, we the audience are content if we are entertained and we haven’t hit the ‘Oh please!’ moment. If you want to know more about this moment, take a look at the book “Hollyweird Science – From Quantum Quirks to the Multiverse” by Kevin Grazier and Stephen Cass. From it, you can make up your own mind on just what you’re ready to accept as entertaining and what is just too much expectation by the storyteller.

The book is available through Springer at this link.