Monday, May 20, 2024

Why don’t asteroids and comets take spherical shapes like stars, planets and moons? | Science


Our solar system and space contain celestial bodies of many shapes and sizes, from tiny dust particles to medium-sized planets and large stars.

Although most objects we know are round, such as planets, stars, and some moons, smaller objects in space such as asteroids and comets have irregular geometries.

But why do these bodies have strange shapes when other bodies take a regular spherical shape?

Planets and stars take regular spherical shape due to gravitational effect in whole universe (NASA).

Gravity dominates the figure

Planets and stars take their spherical shape due to the effect of gravity throughout the universe, where gravity pulls matter toward its center of mass.

Alessandra Springman, a researcher studying asteroids at the University of Arizona’s Lunar and Planetary Laboratory, told Live Science:Direct science) Al-Alami It’s about mass and gravity, where gravity creates large bodies like planets and some moons, and he adds, “If you have enough mass, gravity will dominate your shape.”

When the system becomes large enough, gravity pulls everything equally towards the body’s center of mass and this gravitational force creates a spherical shape. In general, a spherical shape is the most stable structure for a large mass.

What makes asteroids and comets?

In contrast to large objects in space, there are asteroids, comets and other small objects that are not formed by gravity because their mass is small and their gravity is weak and does not affect the shape of their material.

A report by The Science Times (Science Times) Despite the strength of gravity, it is weak because, in physics, a body must reach a certain size in order to exert the pull of gravity and its ability to overcome the strength of its material.

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Small solid bodies have a weak gravitational force that is not enough to form itself into a spherical shape, but when an object attains a spherical shape, here it can be said to be in a state of hydrostatic equilibrium.

Asteroids, for example, are collections of small units that have moved and stuck together over time, so they have bumps and bulges in their outer shape.

In our Solar System, there are some objects in the Kuiper Belt “KPOs” (KPOs) that orbit the Sun after Neptune and are remnants of the formation of the Solar System after most of the planets from which they formed have been consumed. The solar system is the original material, so the gravity of these objects is too small to affect its shape.

Asteroid “Bennu” has a semi-diamond shape rather than a circle due to its small size (NASA).

Other factors

In the absence of the creation of gravitational forces, other factors play a role in giving the final shape to these objects in space, some of which we mention:

  • First: Some asteroids like the KBO Arrokoth asteroid collide with each other and become more lumpy and less round. It looks like two pancakes or two rocks stuck together, so it is sometimes called a snowman. Colliding and sticking.
  • Secondly: The asteroids are “Bennu” and “Ryuku”, and they have semi-diamond shapes, not round, and their shape is due to their geological composition, as they are just piles of pebbles, and they are very porous. They are held together by gravitational or non-frictional forces such as weak van der Waals forces acting on the particles and pulling individual particles together.
  • Third: There’s comet 67P/Churyumov-Gerasimenko, famous for its “rubber duck” appearance, and Springman comets come in strange shapes, not just because of their size, but because they’re often created. Ice, whether it’s water ice or any other type of ice, so as these comets approach the Sun, the ice evaporates into gas, passes through the liquid phase and is ejected into space, and all of these active surface geologic processes lead to some. Strange patterns on the surface.
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A comet that looks like a “rubber duck” (ESA).


According to “The Guardian” newspaper (Guardian) British, the solid, liquid or gaseous composition of the planets affects the possibility of forming a spherical shape with gravity.

For example, planets have high gravity and are mostly liquid or gas, even Earth is just a thin shell of solid rock over a semi-liquid core, so it forms a uniform sphere around its center of gravity.

Planets use liquid and partly solid composition to form solid cores, and the planet’s liquid environment helps it form a spherical shape due to its rotation and other physical phenomena.

As for asteroids, they tend to be clumps of solid matter and have no liquid interiors with their own little gravity, so they can’t become a sphere, but come in all sorts of other odd shapes.

Evidence : Guardian + Direct science + Websites

Nadia Barnett
Nadia Barnett
"Award-winning beer geek. Extreme coffeeaholic. Introvert. Avid travel specialist. Hipster-friendly communicator."

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