How Big Is Uranus?
QUICK ANSWER
Uranus has a diameter of about 31,500 miles (50,720 km), roughly 4 times Earth's diameter. It's the third-largest planet in our solar system, after Jupiter and Saturn. About 63 Earths could fit inside Uranus by volume, though Uranus is much less dense than Earth and only 14.5 times more massive.
Uranus is huge by Earth standards but small for an ice giant. It's the third-largest planet in our solar system, comfortably bigger than Earth but noticeably smaller than Jupiter or Saturn. The interior structure is what makes Uranus different from both rocky and gas planets: a class of its own.
How big is Uranus compared to Earth?
Uranus is roughly four times Earth's diameter. According to NASA, Uranus has an equatorial diameter of about 31,500 miles (50,720 km), compared to Earth's 7,918 miles. By volume, you could fit about 63 Earths inside Uranus. Uranus's mass is 14.5 times Earth's, much less than its size advantage would suggest because Uranus is far less dense than Earth. Uranus's surface gravity is actually slightly weaker than Earth's, despite the planet being so much bigger.
How does Uranus rank among the planets?
Third largest, behind Jupiter and Saturn. Jupiter is the biggest by far (11 times Earth's diameter), Saturn is second (9.5 times), and Uranus and Neptune are tied for third and fourth (both about 4 times Earth's diameter). Uranus is slightly larger than Neptune by diameter, but Neptune is more massive because it's denser. The size order is sometimes confusing because the four giants are often grouped together visually, but Jupiter and Saturn are dramatically bigger than Uranus and Neptune.
What is an ice giant?
A planet category that fits Uranus and Neptune but not Jupiter and Saturn. Ice giants are made primarily of water, methane, and ammonia (which planetary scientists call ices, even though they may be liquid or supercritical fluids inside the planet), with relatively thin outer atmospheres of hydrogen and helium. Gas giants like Jupiter and Saturn are mostly hydrogen and helium throughout. The difference is more about composition than size, but it affects the planets' internal structure, magnetic fields, and weather patterns.
Why isn't Uranus as big as Jupiter?
Because Uranus formed in a different part of the early solar system. Jupiter formed closer to the inner solar system, where there was more leftover gas, and accumulated huge amounts of hydrogen and helium during its formation. Uranus formed farther out, where solid icy material was more abundant but gas was more scattered. Uranus grew large but never got the chance to gather as much gas as Jupiter did before the early solar wind cleared out the surrounding material. The result is a smaller planet with a different internal composition.
Uranus is about four times Earth's diameter and 14.5 times Earth's mass, making it the third-largest planet in our solar system. It's an ice giant rather than a gas giant, meaning its interior is more about water and methane than hydrogen and helium. Uranus is huge by any rocky-planet standard but small compared to Jupiter and Saturn, sitting in its own category.
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