Why do planets,moons and stars all look round like a ball?

Does gravity or a vacum shape them?

20 Answers

  • 1 decade ago
    Best Answer

    gravity pulls everything inward to the center equally.

    imagine gravity being the radius in a circle. the radius will always be the same distance inside the circle, no matter if you spin it. (unless you add more matter, then gravity gets stronger and the radius will increase.)

    so the gravity radius pulls the matter it comes across and packs it into the center on all sides. this works extremely well with dust, liquid or gases which is what planets or stars where before/as they where forming

    asteroids and comets don't exactly look like balls because they supposedly where attached to balls that blew up after they became solid.

    once an object is solid, gravity cannot shape it, because gravity is actually very very weak when compared to such rigid molecular structures as a solid.

    also the fact that everything is "suspended" in space gives room to build an object that has sides in ALL directions such as a ball.

    stars are not really always a spherical structure. They do invovle circular shapes and paths, and some have "disks" that circle around them, and "arms" that shoot out

  • 1 decade ago

    Planets are thought to have accreted from dust particles in space which were pulled towards each other by their mutual gravitational attraction (the dust had already been created by exploding stars). A denser zone of dust would attract more particles towards it because its gravitational pull would be stronger.

    The more mass that a body has the more gravitational force there is to pull it and other objects closer together.

    A planet gradually forms by capturing dust which has impacted into one of these denser zones of dust.

    The Earth isn’t a very rigid body: most of the core is molten and, though its crust is made of solid materials, those materials have limited strength – only enough strength to form mountains a few miles high - that, partly because of their pyramid-like shapes, can just resist the crushing force of their own weight. Think of a sand castle that collapses because it has been built too tall and too narrow in shape.

    As a body increases in size, each of its dimensions increases, but not its strength or rigidity. If you made a miniature bridge out of modelling clay, it might be strong enough to span a gap and support a small weight but if every dimension was then increased to make a ‘practical’ bridge it would just collapse because the strength of the clay material would not have been scaled up by the same amount.

    If the Earth was much smaller, its mountains would make its shape irregular – like some of the asteroids we have seen in pictures. However, the Earth is too large for mountains to make much difference to its shape (if you drew a circle with a pencil on a notepad to represent the surface of Earth, the tallest mountain and the deepest sea bed would still lie within the thickness of the pencil line).

    At springtime, river ice will crack and be swept downstream towards a lake or the Sea. In a similar way, the fragments of the Earth’s fragile crust, floating on the ‘sea’ of the Earth’s molten core, move to the lowest place and stay there. That’s why the Earth - as well as the other planets and moons - and also why the gaseous stars all tend to look like a ball.

    Source(s): Short geology course experience of materials and their strengths
  • 1 decade ago

    Gravity is what shapes stars,planets and moons and they are all spheres.

    However a rocky asteroid could be shaped like any thing,a hot dog or a potato since it's gravity would not be strong enough to sculpt it round.

    It a small asteroid formed form fine dust it could form a sphere since it's low gravity would be sufficient to form a sphere.

  • 1 decade ago

    Gravity. When a planet is pulling itself out of the stellar material that forms a system, it tries to compact itself as small as it can. The smallest shape is can assume is a circle, so invariably planets and stars are spheres.

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  • 1 decade ago

    For the answer we have to go back to the time billions of years ago when the planets were first starting to form within a vast cloud of gas and dust (..called a 'nebula'..) Within that cloud some particles were near enough to each other that they were drawn to each other by their mutual gravity. That in turn increased the gravity of the clump and other particles were drawn in to it from *all directions.* The result was a growing sphere that continued drawing in material from all directions towards its center.

  • 1 decade ago

    Ummm......that would be because they are. Gravity and rotational pull would be the reason that they are shaped in the shape of a sphere

  • 1 decade ago

    Because they ARE shaped round...Gravity pulls the stuff on them evenly towards the center which is why it's round.

  • 1 decade ago

    because they are all round like a ball....

    they become that way because the gravity is equal on all the sides so they build up into a ball.

  • 1 decade ago

    Because the only shape any mass can make with no external influences is a sphere. Raindrops are also spherical. This is because it has nothing to cling to but itself.

    Gravity has nothing to do with it, since very small objects behave the same way (eg, the raindrop).

  • J M
    Lv 7
    1 decade ago

    Because being spherical is a natural state for a mass floating in a void.

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