(ORDO NEWS) — Planets and many space bodies are almost perfectly spherical, but asteroids and comets have different shapes. These objects range from tiny dust particles to planets and massive stars, including our Sun.
Most of the bodies we are familiar with are round, like the Earth, while some of them have irregular geometry. But why do some cosmic bodies have a spherical shape, while others have unusual shapes?
The planets and the Sun are spherical due to the influence of gravity, which is present not only on our planet, but throughout the universe.
The gravitational attraction of a certain material is always directed towards its center of mass. If the material has a large amount of mass, then the gravitational attraction is greater. Despite the fact that gravity exhibits great force, it does not affect the internal properties of matter.
“In short, it all comes down to mass and gravity,” said University of Arizona researcher Alessondra Springmann.
Gravity shapes large objects such as planets and their moons.
“If you have enough mass, gravity will dominate your shape,” Springmann said.
The gravitational force present in solid objects is opposed to their own force. An example of this is the force of gravity we feel on Earth. This force is probably pushing us towards the center of the planet, but contrary to popular belief, the Earth is actually being pushed up and has a lot of force.
The immeasurable power of the Earth also has its limits. This border is manifested by massive objects on the surface of the planet.
For example, Mount Everest gets a little bigger when the Earth’s plates collide with each other. The higher it reaches its peak, the harder it becomes. However, this weight gain has a limit and will eventually sink into the Earth’s mantle. This event limits the height of Mount Everest.
If the planet is completely covered by the ocean, then Mount Everest will simply sink to the center of the Earth and displace a huge amount of water.
As the mountain moves towards the center of gravity, the lowest point of water on Earth will become higher.
This process will result in the oceanic planet’s physical form being perfectly spherical. Once the structure is large enough, gravity pulls everything equally towards the body’s center of mass. This gravitational force creates a spherical shape.
And as for asteroids, comets and other small cosmic bodies, “these objects are made up of leftovers from the formation of the solar system after the growing planets swept away much of the original material of the solar system.
These tiny bodies are too small for gravity to affect their shape,” Springmann said.
When the influence of gravitational forces is reduced, other factors come into play. Some asteroids are lumpier and less round because they collide with each other, Springmann said.
For example, KBO Arrokoth is shaped like two pancakes glued together. Scientists believe that Arrokoth formed from two objects that slowly orbited each other closer and closer until they collided and stuck together.
Meanwhile, asteroids Bennu and Ryugu are rhombus-shaped rather than round. Their shapes are the result of their geological composition.
Bennu and Ryugu are essentially “heaps of garbage,” Springmann said. “It’s just piles of gravel.”
These two asteroids are extremely porous and are held together by forces other than gravity or friction, such as the weak van der Waals force.
The van der Waals force acts on the particles themselves, pulling individual particles together. Scientists suspect these two asteroids are diamond-shaped because their rotational speeds are affected by how the asteroids absorb and emit solar radiation.
Comet 67P/Churyumov-Gerasimenko has the famous rubber duck shape. Comets come in strange shapes, not only because of their size, but also because they are made mostly of ice,” Springmann said.
As comets approach the Sun, this ice sublimates and escapes into space, creating a temporary atmosphere around the comet called a coma.
“These jets can form all sorts of structures on the comet’s surface,” Springmann said. In 67P, “you have all these active surface geologic processes that lead to some weird surface shapes like fissures and fissures,” Springmann concludes.
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