This blue planet is the seventh from the Sun in our Solar System. Uranus spins on its side, so its rings rotate up and down around the planet. This is different from the rings that rotate around the middles of Saturn and Neptune. The planets odd rotation probably exists because of a collision with an object the size of Earth.
Who Discovered Uranus?
Astronomer William Herschel first saw Uranus in 1781 while looking for stars. Herschel initially thought what he was seeing was a comet, so he began to track it. When he reported his findings, a man named Anders Lexell used Herschel’s observations to calculate the orbit. The two astronomers determined that the object must be a planet past Saturn. This made Uranus the seventh planet in the Solar System, and the first found with a telescope.
How Did Uranus Get its Name?
Uranus is the god of the sky and the only planet with a name based on Greek mythology. The planet wasn’t named until 70 years after it’s discovery. William Herschel wanted to name the planet Georgium Sidus after King George. Very few scientists liked this name so it was rarely used. Astronomers thought the name Uranus made sense because it follows the pattern of mythology and planets in the Solar System. In the mythology, Uranus is the Greek version of Caelus. Caelus is the father of Saturn, and Saturn is the father of Jupiter. In the Solar System, Uranus is the seventh planet, Saturn is the sixth, and Jupiter is the fifth.
Gravity on Uranus
Compared to other planets in the Solar System, Uranus has similar gravity to Earth. Uranus’ gravity is 8.9 m/s² while Earths gravity is 9.8 m/s². The gravity on Uranus is only a little bit weaker than the gravity on Earth. For example, if you weigh 100 pounds on Earth, you would weigh about 91 pounds on Uranus.
Why is Uranus Blue?
The atmosphere of Uranus has methane in it. When hit by light from the Sun, the methane absorbs the red light and reflects back the blue light. This reflected blue light is what our eyes are able to see.
What is Uranus Made of?
Unlike other gas giants, Uranus’ mantle is mostly icy water and ammonia. Because of all the ice, the planet is often times called an ice giant instead of a gas giant. The ice in the mantle isn’t like what you find in your freezer, this ice is hot! The ice can’t melt because of the extreme pressure on the planet that squishes molecules together. This forms a kind of hot slush called a water-ammonia ocean. Beneath the ice scientists believe there is a layer of liquid diamond! This forms when carbon in the atmosphere condenses into diamonds and rains down. The best part? The huge solid diamonds floating in the ocean. Beneath the ice and diamond mantle, there is a small rocky core made of iron and nickel. Above the ocean, there is an atmosphere made of hydrogen, helium, and methane gases and an outer atmosphere made of hydrogen.
Uranus appears to be spinning sideways! But, what’s sideways for a sphere?
Unlike all the other planets in our Solar System, Uranus spins on its side. The main theory for the odd rotation is a collision with a developing planet. When the Solar System was young, a runaway protoplanet smashed into the top of the ice giant. The crash was so powerful that it completely changed the direction of Uranus’ planetary rotation.
The collision would also explain Uranus’ inner moons. The protoplanet was likely made of rock and water ice. During the collision, all the debris flew up and got caught in an orbit around the planet. This debris combined to form small icy moons. Uranus’ outer moons are larger and a different material than the inner moons. This leads scientists to believe that the outer moons are actually asteroids that Uranus captured with its gravitational pull.
An up-close photo of Titania, Uranus’ largest moon. (Image Credit: NASA/JPL)
Uranus also has rings, though they don’t stretch out as far as the rings of Saturn. The inner 9 rings contain mostly dark dust particles and large rocks. These dust particles make the inner ring system appear grey. Uranus also has two outer rings, the inner one red and the outer one blue.
A view of Uranus’ rings edge on. Uranus is so bright that the rings disappear as they cross over the planet.