How Big Is Saturn?
QUICK ANSWER
Saturn has a diameter of about 72,400 miles (116,500 km), making it the second-largest planet in our solar system after Jupiter. About 763 Earths could fit inside Saturn by volume. Despite its size, Saturn is the least dense planet, light enough to theoretically float in water.
Saturn is huge, the second-biggest planet in our solar system, but the strangest thing about its size isn't the size itself. Saturn is so light for its volume that it would actually float if you could find a big enough body of water. It's the only planet in the solar system with a density less than water.
How big is Saturn compared to Earth?
Saturn is vastly bigger. According to NASA, Saturn has a diameter of about 72,400 miles (116,500 km), roughly 9.5 times Earth's diameter. By volume, about 763 Earths could fit inside Saturn. Saturn's mass is about 95 times Earth's, though that's less than you'd expect for its size because Saturn is so much less dense than Earth. Saturn is the second-largest planet in the solar system, after Jupiter, which is roughly 20 percent bigger by diameter.
How does Saturn compare to Jupiter?
Saturn is the smaller of the two gas giants. Saturn's diameter is about 84 percent of Jupiter's, and Saturn's mass is about 30 percent of Jupiter's mass. The two planets formed in similar ways from similar materials, but Jupiter accumulated more gas during the early solar system. Both planets are mostly hydrogen and helium, and both have ring systems, though Saturn's rings are far more prominent than Jupiter's. If you put the two planets side by side, Jupiter would look like a larger, more colorful version of Saturn.
Could Saturn really float in water?
Technically yes. Saturn's average density is about 0.69 grams per cubic centimeter, which is less than the 1.0 g/cm³ density of water. That makes Saturn the only planet in the solar system that would float in a sufficiently large bathtub. The low density comes from Saturn being mostly hydrogen and helium, the lightest elements, with relatively little rock or metal compared to the rocky planets. The floating fact is a fun thought experiment but doesn't have any practical application, since there's no body of water big enough.
Why is Saturn so much less dense than Earth?
Composition. Earth is a rocky planet built mostly of iron, silicon, and heavier elements that pack tightly together. Saturn is mostly hydrogen and helium, the two lightest elements in the universe. Even though Saturn's gravity compresses its interior significantly, the underlying material is so light that the average density stays low. Jupiter is also mostly hydrogen and helium but has enough mass to compress its core into much denser material, which is why Jupiter is denser than Saturn despite the similar composition.
Saturn is the second-largest planet by size, with 763 Earths fitting inside it, but it's the least dense planet in the solar system. The low density is what gives Saturn its famous would-float-in-water property. Among the planets, Saturn is the one that's huge but unexpectedly lightweight, with a structure built almost entirely from the simplest elements in the universe.
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