Why Are Planets Almost Spherical? (Are you listening flat-earthers?)

Posted by K R on

It's something we kind of take for granted. Roses are red, and planets are spherical. That's just the way things are, right? After all, building model solar systems would be way more challenging if, instead of using little foam balls, we had to make a bunch of icosahedron-shaped planet models. But have you ever wondered why the planets look like this? Why are they basically spherical and not, say, cylindrical or cube-shaped? We should kick off this discussion by calling a spade a spade. None of the planets in our solar system are perfect spheres, nor for that matter is our sun. All those bodies could more accurately be described as "oblate spheroids." Objects with this shape bulge slightly around the middle. To borrow an analogy from the astronomer Phil Plait, they look like a basketball that someone is sitting on. Put more technically, in a celestial body with an oblate spheroid shape, the polar circumference will be smaller than the equatorial one. So here on Earth, if you were to travel from the North Pole to the South Pole and back, you'd have walked a grand total of 24,812 miles (39,931 kilometers). On the other hand, a complete trip around the equator would be a bit longer. That's because the circumference of Earth's equator is 24,900 miles (40,070 kilometers). As such, when you stand at sea level on the equator, you're farther away from the center of our planet than you would be at either pole. On some other planets, this bulge is even more pronounced. Just look at Jupiter. Earth is only 0.3 percent wider at the equator than it is from pole to pole. But Jupiter's measurements showcase a much bigger disparity. Indeed, astronomers have found that this plus-sized planet is a full 7 percent wider at its equator than it is between the poles.

Read More: HowStuffWorks

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