Asked by: R N Hadley, South Africa
Yes, and we’re sitting on one. The Earth is not a perfect sphere – it’s an oblate spheroid. In other words, it’s a sphere in which the diameter at the equator is greater than that between the poles. This ‘equatorial bulge’ is caused by the Earth’s rotation. It makes Earth’s diameter at its equator about 42km (26 miles) greater than at its poles. Jupiter’s shape is flattened even more significantly. It’s the fastest rotating planet in the Solar System and has a bulge of over 10,000km (6,214 miles).
Though not perfect spheres, bulging planets are symmetrical around the axis running through the poles. So you could argue that they’re not really irregular. Other bodies like asteroids and comets can be highly irregular. Eros is a large asteroid about 34km (21 miles) in length, resembling a peanut. In even larger bodies, rotational forces overwhelm the strength of their constituent rock. Then, you end up with spherical objects like Ceres. With a diameter of nearly 1,000km (621 miles), it’s considered a small planet.