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Join SciShow Space as we complete our tour of the Solar System planets with the ice giants, Uranus and Neptune.
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Sources:
http://www.lpi.usra.edu/decadal/opag/IceGiantAtmospheres_v7.pdf
http://www.lpi.usra.edu/opag/outer_planets.pdf
http://astronomy.nmsu.edu/tharriso/ast105/UranusandNeptune.html
http://news.discovery.com/space/astronomy/jet-streams-on-the-ice-giants-13052.htm
http://www.universetoday.com/22076/uranus-and-neptune/
http://www.space.com/18922-neptune-atmosphere.html
http://www.space.com/18708-uranus-atmosphere.html
http://www.space.com/13248-nasa-uranus-missions-solar-system.html
http://www.space.com/18921-neptune-temperature.html
*Intro music*

We've come to the end of our journey through the Solar System's planets, a trip in which our hypothetical explorers haven't fared too well. Death while visiting the previous five planets have come in the form of heat, cold, radiation, lack of oxygen, lack of any surface, and bone-crushing pressure, just to name a few. 

And we won't do much better on the ice giants Uranus and Neptune. The only two planets invisible to the naked eye from Earth and perhaps, unsurprisingly, the two we know the least about. Voyager 2 is the only probe to ever get close to either planet. Making flybys of Uranus and Neptune in the late 1980s. And between Voyager 2's data and studies using telescopes, scientists have pieced together quite a bit.

Earth and Venus are often described as twin planets, but Uranus and Neptune are the real siblings of the Solar System, with their similar size, mass and composition. Both are around 50,000 kilometers across. Both have about 15 times as much mass as Earth, and both contain roughly the same breakdown of gases. The freezing cold upper atmosphere's of both planets are dominated by hydrogen and helium, which make up about 20% of the planet's masses. You'll also find plenty of methane. 

It's this methane that actually gives Uranus and Neptune their distinctive blueish hues. As sunlight passes through the outer layer of haze, the methane absorbs red and orange light, reflecting the bluer end of the spectrum. 

Dive deeper and eventually you'll hit the icy mantles. These mantles surround the cores and are made of methane, ammonia, and water. At over a thousand degrees Celsius it's pretty toasty in there, but the pressure is high enough to force the molecules into a slushy form of ice. Despite their similarities, there are still a lot that makes these planets different. So let's take a look at Uranus first.

More than 2.8 billion kilometers from the Sun, and locked in an orbit that lasts 84 Earth years. Oddly enough, it's the coldest planet in the Solar System, even though it isn't the farthest from the Sun, with average temperatures hovering around negative 224 degrees Celsius. Usually, planets are warmer when they produce more heat than they get from the Sun, but Uranus doesn't generate much internal heat of its own, so it stays cold. That lack of internal heat should mean than the planet doesn't have much by way of weather, except when the seasons change at the equinox, because that's when the equator gets the most sunlight. 

But those seasons don't change often, thanks to the strangest rotational axis of any planet in our Solar System. Uranus is tilted 98 degrees, so the planet looks like it's spinning on its side, more like a ball rolling around the Sun than a spinning top. That weird tilt means that 42 years at a time, one of the planet's poles is continuously facing the Sun, while the other side is in complete darkness. That's over four decades of night. Astronomers believe Uranus got knocked over by a collision with a protoplanet billions of years ago, when the Solar System was still forming. They also think that's what messed with the planet's internal heating, and therefore its weather. 

The last equinox was in 2007, and scientists did notice larger weather patterns in Uranus' atmosphere. Infrared images of the planet have revealed occasional cyclonic storms with winds that can eclipse 900 kilometers an hour. Once the equinox was over, researchers expected Uranus to become boring and weatherless again, but it didn't. In 2014, observations using the Hubble and Keck II telescopes showed giant storms scattered across the planet's northern hemisphere, and astronomers still aren't sure what fueled them. 

Speaking of crazy weather, let's continue to Neptune with is 4.5 billion kilometers from the Sun. As result, it receives 40% as much sunlight as Uranus, which you'd think would make it cold and boring, but that is not the case. There are some strange things happening on our 8th and final planet. 

In stark contrast to Uranus, Neptune has some the most extreme weather in the Solar System. Winds top out at more than 2,100 kilometers an hour - the fastest found on any planet - with storms that last for months and even years. Scientists believe the weather is thanks to plenty of heating from Neptune's core, and despite being nearly twice the distance from the Sun as Uranus, its average temperature of negative 218 degrees Celsius makes the planet slightly warmer. 

It would be nice if we could take a closer look, but in these gaseous icy outer reaches of the Solar System, our options are kind of limited. And so, our imaginary probe ends its tour of the Solar System planets with an icy, windy plunge. So thanks for exploring the Solar System with us here on SciShow Space, and especially thanks to our Patreon patrons who help make this show possible. Thank you again, and don't forget to go to youtube.com/scishowspace and subscribe.