Uranus, the ice giant. This cold, bluish grey marble seems like adesolate waste in the far reaches of the solar system, but in actuality there are some fascinating facts about this planet which makes it unlike anything else in the solar system.
Stick with me on this journey and we willexplore everything you could want to know about Uranus. All the planets are named after Roman gods,except for Uranus. It’s named after the Greek god of the sky,Ouranos.
The Latinised version of this word is whatwe use today, Uranus. Had they just kept the Greek version, it mighthave saved a bit of embarrassment as people stumble over saying Uranus in a polite way.
It even has two ways to pronounce it as no-onehas been able to definitively agree on the matter, Uranus and Uranus.
Uranus is also very special in the way itrotates and orbits. It is the 7th planet from the Sun, the secondfrom last planet. It orbits on average around 19.2 AU from the Sun, which means it is over 19 times further away from the Sun than our Earth.
This varies throughout its year by 1.8AU,the biggest difference of any planet. Being this far away from the Sun means itis freezing cold.
As in at the upper atmosphere, -220c cold,the coldest planet in the solar system. Its year lasts 84 Earth years. When it was first observed,
astronomers predictedits orbit. After some time though, they realised it hadn’tfollowed their predictions, and concluded the reason was because there was another planetthat had a gravitational influence on it.
They predicted where this planet should beand as a result, Neptune was discovered. Interestingly,
the same theory surrounds this“Planet X”. Some far out objects in our solar system arenot where they should be, and theory suggests this is because of another planet that hasa gravitational influence on them.
The hunt is now on to actually find this planet! Now, what’s really interesting about Uranusis its rotation. Most planets rotate like a spinning top onthe table of the solar system plane. Not Uranus, no Uranus has fallen over andis rolling instead.
This means its seasons are crazy in comparisonto the rest of the planets.
During its solstice, the time of year whenthe Sun is highest or lowest in the sky, one side of the planet always faces the Sun whilethe other is complete darkness. It kind of looks like the planet is rollingforward along its orbit.
Only a very narrow strip near the centre ofthe equator of the planet experiences day and night during this time, but the sun onlyrises just above the horizon. The poles get 42 years of continuous darknessfollowed by 42 years of daylight. During its equinox, the opposite of a solstice,the planet has more of a normal day-night cycle. Uranus rotates once every 17 hours and 14 minutes.
Because its surface is not solid though, someparts of the atmosphere rotate faster than others, and due to high winds, some partscan make a full rotation of the planet in only 14 hours. This strange rotation means it is the onlyplanet that gets more energy from the sun at its poles on average than its equator.
For some reason though, the equator it hotterthan at the poles, and no-one really knows why. Speculation also exists as to why Uranus rotatesthe way it does in the first place, although it is generally accepted that a large earthsized planet crashed into Uranus, knocking its rotation on its side.
How big actually is Uranus? Well it is the least massive of the gas giants,at 14.5 Earths compared to Neptune’s 17 Earth masses. Its diameter is just bigger than Neptune’s though at 50,700km, about 4 times more than Earth’s.
Because this mass is spread out over a largearea, the gravity on Uranus is only slightly less than on Earth, at 8.7m/s2 or 0.89g. Quite comfortable! And what is it made of? Well it has a rocky silicate material smallerthan earth at the core, which is surrounded by a mantle of water, ammonia and methaneices.
Although it’s referred to as ices, thismantle is in fact very hot, reaching almost 5000c, and is more like a liquid ocean surroundingthe core.
The atmosphere is in comparison very insubstantial,only consisting of a total of 0.5 Earth masses, most of the mass of Uranus being in the coreand mantle.
The atmosphere is comprised of mostly helium,hydrogen and 2.3% methane and then a cloud layer on top. It’s this methane that give Uranus it’saquamarine or cyan colour.
Very interestingly, some models suggest thatthe pressure at the base of the mantle on Uranus is enough to break apart the methanemolecules apart, which then compresses the carbon atoms into diamonds.
These diamonds rain through the mantle likehailstones. Unbelievably, the very base of the mantlecould be a layer of liquid diamond, with solid “diamond-bergs” floating in it. To me, that's a bit difficult to wrap my head around! We’ll fly away from the planet just a littlebit now to have a look at its planetary ring system.
Uranus, much like the other larger planetsin our solar system, has rings.
It has thirteen, very dark and young rings.
Most are not bigger than a few kilometreswide and they are thought to only be 600 million years old, much younger than Uranus. They are comprised of extremely small particles,the biggest being only a few meters across, made of water ice and dark radiation_processedorganics.
Their albedo doesn’t exceed 2%, or in otherwords, darker than wet soil. As we’ll see shortly, Uranus has a lot ofmoons, and the rings are thought to be the result of high impact collisions of some moonsin the past.
It is unclear why some of the rings are keptso narrow, the usual explanation being that the rings are being kept in line by shepherdmoons, but this is only the case for one of the rings.
Uranus was first discovered to have ringsin 1977 when an occultation of a star occurred.
The star dimmed a few times on either sideof Uranus as Uranus moved in front of it, confirming the presence of rings.
Uranus has only been visited by spacecraftonce, and that was in 1986 by Voyager 2. Voyager 2 discovered a lot of the rings andmoons of Uranus, giving us close up shots of the faint ring systems. When Voyager flew by though, this only broughtthe total of known rings to eleven. When Hubble was launched, it also had a lookat Uranus, discovering two additional rings that had never seen before.
The outermost ring is twice as far away fromUranus as the previously thought outermost ring.
And as promised, here is a look at the manymoons! Unusually, the moons are named after figuresin English literature.
Overall, Uranus has 27 known moons dividedinto three categories, the thirteen inner moons, five major moons, and nine irregularmoons. The inner moons are connected with the ringsof Uranus, some of which may have provided the rings materials. The largest of these moons is called Puck,at only 162km in diameter.
It is the only of the inner moons to be capturedin detail by Voyager 2. Interestingly, these inner moons constantlyperturb each other and the system seems very unstable.
There’s a good chance some of them may collideagain in the future.
The five biggest moons, in order of distancefrom Uranus starting on the left are Miranda, Ariel, Umbriel, Titania, and Oberon. Titania is the largest moon of Uranus and the eighth largest moon in the solar system, at 1,600km.
Again, as can be seen, these are very darkobjects, Umbriel being the darkest. With the exception of Miranda, which is comprisedmainly of water ice, the rest are thought to be a mix of water and rocky materials.
These moons may have differentiated interiors,meaning a core of rocky material with a mantle of ice. Between the core and the mantle could wellbe a layer ocean of liquid water. Interestingly, the axial tilt of the largemoons is the same as Uranus, meaning that during solstice, if you were to look at theSun, it would only ever move in a circle in the sky, never setting.
During solstice, only one side of the moonfaces the Sun, meaning a constant daytime. It has nine moons.
They are likely to be captured objects andare much further out than the last of the big moons, Oberon.
They vary in size from 20km to the biggest,Sycorax, which is about 200km in diameter. Finally, let’s explore Uranus’ climateand magnetosphere.
Uranus’ seasons are quite unique in thesolar system due to its exceptional axial tilt. We only have data for about one Uranian yearthough, which means it’s difficult to be able to say with certainty differences betweenthe years. What has been observed is that as the planetapproaches solstice, the pole brightens and a collar forms.
Moving away from solstice, the pole and collardim.
This brightness is thought to be because ofthickening of methane clouds, although the cause is not clear. Storms are relatively rare on Uranus comparedto the other gas planets, but are thought to be caused by changes in the seasons. And another unique feature of Uranus is itsunusual magnetosphere.
Usually magnetospheres originate from thegeometric centre of the planet, but that’s not the case with Uranus. Also, it’s not in line with the rotationalaxis, but is 59 degrees off. This unusual placement means the magnetosphereis much stronger at the north pole than at the south.One theory for this is the liquid diamondocean could deflect the magnetosphere, or even that it is not the core of the planetthat produces the magnetosphere but rather the water mantle.
The magnetosphere is about as strong as Earth’s,and because of its unusual rotation, the magnetotail corkscrews off for millions of km into space. Thank you so much for watching, I hope you’velearned more about this rather mysterious planet.
I was dreading to write article on Uranus bit becauseI was wondering what I can actually talk about. Having done the research though, I found itone of the most interesting planets I’ve covered so far.
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