Gravity makes rocks and water and other things move from higher regions to lower regions, so over time the planet becomes more spherical. The asteroids usually do not have enough gravity and have irregular shapes.
Kieran’s right. Remember also that the pressures and temperatures involved in something as big as the earth are huge and much of the earth is molten rock, so can change shape easily. We don’t see that, normally, and think of rock as hard, but on a planet scale it’s simple. Gravity attracts, and things are as close to each other as they can be in a sphere.
Gravity is an equal force in all directions and it pulls towards the centre of the star or planet which means the material is pulled into a sphere. Though planets aren’t really shaped like a ball because they spin and this makes them fatter at the equator.
I’m not an astronomer, but I always thought that planets weren’t perfectly spherical. I think the shape of planets changes ever so slightly as well. Take the earth for example. The water on earth moves as tides because of the gravity pull of the moon. As the moon orbits the earth, water on the side of the earth closest to the moon is pulled by the moon’s gravity, forming a water bulge.
The same thing happens to the solid part of the earth too, although the effect of the moon on “earth tides” is much more subtle than “water tides”. Some scientists have collected evidence that “earth tides” due to the gravitational pull of the moon may even contribute to earthquakes, but I think we need a bit more information about that theory
One of the requirements of being a planet is that it is capable of becoming round due to the forces of its own gravity. Planets are large objects with a large mass, so they have a large gravitational force pulling inward toward the centre of the planet. Things like mountains and valleys mean that planets are not perfectly spherical, but the force of gravity keeps them basically round.
Gravity makes rocks and water and other things move from higher regions to lower regions, so over time the planet becomes more spherical. The asteroids usually do not have enough gravity and have irregular shapes.
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Kieran’s right. Remember also that the pressures and temperatures involved in something as big as the earth are huge and much of the earth is molten rock, so can change shape easily. We don’t see that, normally, and think of rock as hard, but on a planet scale it’s simple. Gravity attracts, and things are as close to each other as they can be in a sphere.
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Gravity is an equal force in all directions and it pulls towards the centre of the star or planet which means the material is pulled into a sphere. Though planets aren’t really shaped like a ball because they spin and this makes them fatter at the equator.
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I’m not an astronomer, but I always thought that planets weren’t perfectly spherical. I think the shape of planets changes ever so slightly as well. Take the earth for example. The water on earth moves as tides because of the gravity pull of the moon. As the moon orbits the earth, water on the side of the earth closest to the moon is pulled by the moon’s gravity, forming a water bulge.
The same thing happens to the solid part of the earth too, although the effect of the moon on “earth tides” is much more subtle than “water tides”. Some scientists have collected evidence that “earth tides” due to the gravitational pull of the moon may even contribute to earthquakes, but I think we need a bit more information about that theory
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One of the requirements of being a planet is that it is capable of becoming round due to the forces of its own gravity. Planets are large objects with a large mass, so they have a large gravitational force pulling inward toward the centre of the planet. Things like mountains and valleys mean that planets are not perfectly spherical, but the force of gravity keeps them basically round.
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