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How Big is Uranus?

Uranus and Major Moons
Uranus and its five major moons are depicted in this montage of images acquired by the Voyager 2 spacecraft. The moons, from largest to smallest as they appear here, are Ariel, Miranda, Titania, Oberon and Umbriel.
Credit: NASA/JPL

The seventh planet from the sun, Uranus is the smallest of the gas giants. The blue body contains an icy atmosphere that, like Neptune, differs dramatically from the other large planets.

Radius, diameter and circumference

The mean radius of Uranus is 15,792 miles (25,362 kilometers), giving a diameter four times that of Earth. But like many other bodies in the solar system, the rapid spin of Uranus causes a slight bulge around the center. At the poles, Uranus has a radius of 15,517 miles (24,973 km), but at the equator, it expands to 15,882 miles (25,559 km). This bulge gives Uranus a shape known as an oblate spheroid.

If you were to take a walk around the equator of Uranus — a trip that might be challenging since the planet has no solid surface — you would travel 99,018 miles (159,354 km).

Density, mass and volume

Although Uranus, discovered in 1781, is only four times the physical size of Earth, it is significantly more massive, weighing in at 86 septillion kilograms (just under one trillion trillion trillion). That makes it more than 14.5 times as massive as our rocky home.

The planet has a volume of 6.83x1013 cubic kilometers.

The density of Uranus is 1.27 grams per cubic centimeter, making it the second least dense planet in the solar system. Its low density indicates that it is predominantly composed of ice rather than gas. The icy composition of Uranus and Neptune both differ from the heavier gas giants, Jupiter and Saturn, and have caused them to be labeled "ice giants." The distance to Uranus from the sun is significant, resulting in the coldest atmosphere in the solar system and accounting for the icy temperatures.

Ring around the planet

Although not as famous as Saturn, Uranus does display a set of rings around its middle. The rings around Uranus are made up of tiny dark particles smaller than a meter. Only two of the 13 rings are larger than six miles across.

Although the second ring system to be discovered, the rings around Uranus weren't found until 1977, when astronomers attempted to study the planet's atmosphere as it crossed in front of a bright star. Instead of gradually fading out, as a body with an atmosphere would do, the star disappeared and reappeared several times, indicating rings. It wasn't until NASA's Voyager 2 visited Uranus in 1986 that the rings were imaged.

The rings of Uranus encircle the equator of the planet, but to observers on Earth, they appear to stand almost straight up and down. This is because the planet is tipped almost completely on its side in relation to the plane of the solar system. Scientists think a collision soon after Uranus' formation caused the intriguing misalignment.

— Nola Taylor Redd, SPACE.com Contributor

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