The Ice Giants

In Partnership with Barlow Planetarium

The Two Ice Giants: Neptune (lower right) and Uranus (upper left)

No, that is not a reference to a fairy tale or a comic book. This is about the outermost planets in our solar system: Uranus and Neptune!

Jupiter and Saturn get a lot of attention because Jupiter is the biggest and Saturn has cool rings and both have had missions dedicated to them. Cassini went to Saturn, and Galileo and Juno went to Jupiter. Except for a flyby from Voyager 2 in 1986 and 1989, no missions have gone to Uranus or Neptune. This means that there are still a lot of mysteries about these two planets, but let's talk about some of the cool stuff we do know!

Both planets have a blueish hue due to the gases that make them up. They have hydrogen and helium (like Jupiter and Saturn), but what makes them both look blue is methane gas. Methane absorbs red light, leaving behind the green and blue light. Older pictures made them look more blue, but in reality, they just have a faint blue hue.

Let's talk a bit about each planet 

While they look similar, they're not the same...

Uranus (upper left)

Uranus was thought to be a comet the first time it was seen, but later, William Herschel realized it was a planet. He wanted to name it after King George, but instead they named it after the Greek god of the sky. 

Uranus is the world on its side. It rolls around in its orbit like a barrel, it has rings and 28 moons.

It is about four times bigger than the Earth and is 1.8 billion miles away from the Sun. It takes 84 years for Uranus to go around the Sun one time, and summer and winter each last 21 years.

Neptune (lower right)

Neptune is the only planet in our solar system discovered with math! After Uranus was discovered, its orbit didn't match calculations, so a French mathematician named Urbain Joseph Le Verrier suggested that there might be another planet messing with Uranus' orbit. He was right!

Neptune takes 165 years to orbit the Sun one time, and sometimes, it's farther away from the Sun than Pluto! Because of Pluto's strange orbit, it gets closer to the Sun for 20 years every 248 years.

Why are they called the ice giants? 

Well, that's because, underneath the gases, most of the planets are made up of a mixture of "icy" materials like water, methane and ammonia. They might have a small, rocky core. And, even though the atmosphere is very cold (-200 degrees), at the core, it gets close to 9,000 degrees!

These two planets still have many mysteries to discover and hopefully, we'll get a chance to learn more about them in the future.

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Dr. Teri Gee is the Manager of the Barlow Planetarium in Menasha, Wisconsin. The Barlow Planetarium offers weekly public Star Shows and Laser Shows, along with family events, educational programming, and field trip experiences that inspire a love of science and the night sky. Learn more about Barlow Planetarium at barlowplanetarium.org.