Hi everyone. As you know, last time we took a look at 10 things you wanted to know about Neptune. This time, I thought it would be a great idea to consider some of the things you might find interesting regarding Neptune’s neighbor. Uranus.
- 1. What basic facts do we know about Uranus?
At 2.88 billion kilometers, (1.79 billion miles) away from the Sun, Uranus is the 7th planet you come to. She is also the 3rd largest, being very similar in composition to Neptune. She is the only planet to be named after one of the Greek gods, not Roman.
Note: Interestingly, both Uranus and Neptune have a vastly different composition to Jupiter and Saturn. They are termed Ice Giants, as opposed to gas giants.
This is quite fitting in the case of Uranus, as she has the coldest planetary atmosphere of them all, with temperatures of 49K (-224.2⁰C)
- 2.How big is Uranus?
With a diameter of 51.1 thousand kilometers (31.7 thousand miles), Uranus is four times as large as the Earth, as you can see in the comparison picture below.
She revolves on her axis one every 17 hours and 14 minutes, and takes 84 Earth years to complete one orbit.
- 3.Some of the other giant planets have ‘Great Spots’. Does Uranus have them too?
Uranus is notoriously feature-free. Although she does have bands, they are not as distinct as in the other giants. Scientists think this is due to the complex layers of her cloud structure, which keep the various gases in a constant state of flux.
Note: Remember, another factor could be the fact that Uranus’s internal heat is markedly lower than any of the other giants. (Neptune, which is much further away, radiates 2.61 times as much energy as it receives from the sun back into space) In contrast, Uranus radiates hardly any heat at all.
Scientists are still unsure why this is. One hypothesis is that the planet was struck by a ‘supermassive impactor’ in the early stages of its formation, causing her to expel most of her primordial heat. Another theory suggests some form of barrier has been created within the complex layers of her atmosphere, which prevents the core’s heat from ever reaching the surface.
- 4.What is Uranus composed of?
The upper atmosphere consists mostly of hydrogen and helium with the rest being made up of methane gases. As you go deeper into the mantle, you find water, ammonia, and methane ices. At the core are silicates and nickel-iron rock.
- 5.Any other cool facts?
There certainly is. Because Uranus is so far away, she is the furthest planet from the Sun that can be seen with the naked eye. However, in the past, ancient observers never realized Uranus was a planet because of how slowly she moved through the sky.
- 6.How many moons does Uranus have?
She has 27 known natural satellites. The names for each one have been selected from the works of Shakespeare and Alexander Pope. Of all the planets, Uranus’s moons are the least massive. In fact, the combined mass of the five main satellites – Miranda, Ariel, Umbriel, Titania, and Oberon – would amount to less than half that of Triton, Neptune’s largest moon.
In fact, Titania, the 8th largest moon of the Solar System, is still less than half the size of our own Moon.
- 7.I’ve heard Uranus is tipped on her side? Is that right?
It certainly is. Uranus has an axial tilt of 97.77⁰, so it’s axis of rotation is approximately parallel to that of the plane of the Solar System. Visualize it like this. When most planets rotate, it’s like a globe on a plinth, with a bar running from top to bottom. But with Uranus, she spins on her side, like a ball being rolled across the ground. So, her poles are where other planets equators are. Weird!
Note: Want to hear something else strange? Near the time of the Uranian solstices, one of the poles will receive about 42 continuous Earth years of light, whereas the other side will be in darkness for that length of period. So basically, the poles receive vastly more energy from the sun than anywhere else on the planet’s surface. But guess where the hottest spots of the atmosphere exist? Yes, you’ve guessed it, the equator.
And scientists can’t explain why this is.
- 8.Does Uranus have a ring system like the other giants?
Although very dark and indistinct, Uranus does have a ring system.
At the moment, 13 distinct rings have been discovered, however all but two are very narrow. They are also known to be very young. Dynamic considerations indicate they most likely formed some considerable time after the formation of the planet itself, following the destruction of a moon.
- 9.Does Uranus have an impressive magnetosphere?
Well, she certainly has a peculiar one. Firstly, the Uranian magnetosphere does not originate from its geometric center. Secondly, it’s tilted 59⁰ from its axis of rotation. Not only that, it’s also shifted toward the south by as much as a third of the planetary mass.
Remember – Neptune also has a displaced magnetic field, suggesting this might be a common feature of Ice Giants. (The magnetic fields of terrestrial and Gas Giants are generated by their planetary cores. However, an Ice Giant’s is generated by motion at a relatively shallow depth). Despite this odd feature, the Uranian magnetic field works in much the same way as any other planet.
NOTE: The ladies will love this little snippet. Some scientists believe that there are oceans – and yes, I said oceans – of liquid diamonds within Uranus’s interior that might deter the formation of a magnetic field.
(I told my wife about this…she’s already on the way there…)
- 10.How was Uranus discovered?
Well, as I mentioned during the article, Uranus was actually observed on many, many occasions prior to being ‘discovered’. Because she was so dim and moved so slowly through the sky, observers though she was a distant star, or other astronomical phenomenon. Sir William Herschel, Uranus’s eventual discoverer, also fell into that same trap. He first spotted her on March 13th 1871. Like many others, he mis-reported his findings, stating he had found a comet. Thankfully, when he tried to report his discovery, he received a flummoxed reply, prompting him to check things much more closely. He was glad he did.
NOTE: In recognition of his achievement, King George III of England gave Herschel a stipend of two hundred pounds – (A princely sum in those days) – on the condition that he move to Windsor so that the Royal Family could get a chance to look through his telescopes. He was also nominated ‘The King’s Astronomer’ – not to be confused with Astronomer Royal…
And…They really are cool! I’ve had the pleasure of visiting The Herschel Museum of Astronomy, and witnessing many of the fine instruments he made.
So, there you go. I hope you enjoyed our latest skip about the solar system.
Next time, I thought we’d take a closer look at places where exciting discoveries are being made regarding an important indicator of life…water!
See you then.