Why do asteroids and comets have such bizarre shapes?

Why do asteroids and comets have such bizarre shapes?

While the planets are almost perfectly spherical, the smaller pieces of the solar system, such as asteroids and comets, have very different shapes. But why is this happening?

It’s all about mass and gravity, said Alessondra Springmann, a researcher studying asteroids at the Lunar and Planetary Laboratory at the University of Arizona. Gravity shapes large objects, such as planets and some moons. “If you have enough mass, gravity will dominate your shape,” Springmann explained.

As soon as a structure becomes large enough, gravity pulls everything evenly toward the center of the body. This gravitational force creates a spherical shape, he writes LiveScience.

Then there are asteroids, comets and other small bodies in the solar system, such as some Kuiper Belt objects orbiting the Sun beyond Neptune.

Bodies too small for gravity to affect their shape

These objects are made up of remnants from the formation of the Solar System, after the rising planets swept away most of the original material of the solar system. These bodies are too small for gravity to affect their shape, Springmann said.

Not being shaped by gravitational forces, other factors come into play. Some asteroids are heavier and less round because they collided with each other, Springmann said. KBO Arrokoth, for example, is shaped like two pancakes glued together. Scientists believe that Arrokoth consisted of two objects that slowly revolved around each other, closer and closer, until they collided and stuck to each other.

Meanwhile, the asteroids Bennu and Ryugu are diamond-shaped rather than round. Their shapes result from their geological composition. Bennu and Ryugu are “piles of rubble,” Springmann said.

Made up of remnants from the formation of the solar system

These two asteroids are extremely porous and are held together by forces other than gravity or friction. Scientists suspect that these two asteroids are shaped like diamonds because their rotational speed is affected by the way asteroids absorb and emit radiation from the Sun.

Then there is comet 67P / Churyumov-Gerasimenko, which has the shape of a rubber duck. Comets have strange shapes not only because of their size, but also because they are mostly made of ice, Springmann said. When comets approach the Sun, the ice becomes gas, jumping over the liquid phase and throwing itself into space, forming a temporary atmosphere around the comet.

“These jets can form all sorts of structures on the comet’s surface,” Springmann concluded.

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