Are there any planets in the universe that aren't round?

Every planet in our solar system is essentially round. But out in the universe, are there any planets that aren't spherical?

Technically, planets are round, by definition; they need to have enough mass to produce the gravity required to pull themselves into a spherical shape.

"Actually, one of the specifications for being a planet is, they have enough mass that makes them round," Susana Barros, a senior researcher at the Institute of Astrophysics and Space Sciences in Portugal, told Live Science.

But that doesn't necessarily mean planets are perfect spheres. "We call them round, but they're not really perfectly round, including our own Earth," Amirhossein Bagheri, a planetary Science and geophysics researcher at the California Institute of Technology, told Live Science.

Earth and planets like it often have a bulge around the equator caused by centrifugal force, the outward force experienced by an object that's spinning. On Earth, the bulge is slight but significant: Due to differences in centrifugal force and the distance from Earth's center, things weigh about 0.5% less at the equator than they do at the poles.

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But this effect can be dramatic in the right circumstances. "If the planet is rotating very fast, the poles will flatten," Barros said, leading to a squished, football-like shape.