Why are all planets spherical?

Answer 1

The shape of small objects (like people and houses and mountains and small asteroids) are determined by their mechanical properties. You can take a rock and cut it into a particular shape and it will pretty much stay that way.

The larger the object, though, the stronger its gravitational field. Imagine that you want to build a really tall building. You have to make sure it has a really strong foundation, or the foundation will be crushed by the weight of the building and the building will fall. If there was anything really big sticking up on a planet or a star, gravity would pull it down.

If a planet was like a cube, the corners of the cube would be higher than the rest of the planet. Since planets and stars are so big, you cannot build a "foundation" strong enough to hold up those corners! Anything you built it out of would be too weak to hold them up. Gravity would eventually pull them down.

Even solid rock will flow like a liquid, although very slowly, if it is pulled by a very strong gravitational force for a very long time. Corners on a cubical planet or star would eventually just squish down.

Since gravity pulls toward the center of the planet or star, everything gets pulled down into a sphere. However, planets and stars are not really perfect spheres. They spin, so they bulge out a little around the equator.

Answer 2

Gravity attracts matter in all directions, and a sphere is the only form (shape) that is the same with any orientation.

Actually, planets are not perfect spheres. Because of their rotation, most planets have a bulge near their equator due to the planet's rotation and the centrifugal forces produced by the rotation. The centrifugal forces are greater near the equator because the surface is moving faster (tangencial velocity) at this latitude. At the poles, there is no centrifugal force.

If you travel to the equator, you will actually weigh less than if you were at the poles (altrough the effect is so small you are unlikely to notice any difference, unless you have a very precise scale). This is one of the reasons why space launches are typically done as close to the equator as practical.

Answer 3

In space, the force that pulls planets together is gravity. As a planet grows, the gravity grows and more or less uniformly in all directions so you have a uniform gravitaional field pulling objects in from all directions, this results in a sphere. When a planet gets full size gravity tends to remove any non-spherical aborations as it pulls uniformly to the center.

Answer 4

You might also add our sun and moon. Why is it that they all are the shape of a sphere?

The answer lies in the heat energy contained within them. Were you to release a square ice cube in the space station, it would soon melt and then form a perfect sphere. What has done it is the heat energy.

The reason heat energy acts as it does is expressed in the physics trilogy. E = mc2, m = E/c2, and c2 = E/m describe the basis of our physical existence. The last equation is that of a field of physical time, or a gravitational field - they describe the same force. A large solar mass, having a great amount of heat contained within continually releases energy according to the c2 = E/m concept. Our planet releases an equivalent mass of 0.00444 kg per sec in order to maintain its gravitational field. Our sun expends 665 lbs per sec in order to keep the planets where they should be.

Gravitons ( = c = h ) forming within our planet pass through the center of our world, thus attracting the mass in the direction from which they (the gravitons) had come. They also attract the heat energy within our planet toward its very center. Were this not so, our planet would soon be nearly the same temp. throughout. An example of mass attraction within our planet attracting other mass within it may be found in the mass location that keeps us of the United States in place. It is the mass within the Indian Ocean area. Conversely, the mass below the United States keeps the waters of that region where they belong.

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Answer 5

Interesting question.

One, planets are spherical by definition. An astronomical body that is not spherical is not a planet, it is an asteroid.

And, gravity causes an object of sufficient size to form into a spherical shape... as demonstrated by the recent debate over Pluto and Charon (Pluto's 'moon'), not all objects large enough to form sphere's are necessarily 'planets'. Pluto and Charon being dubbed something like 'sorta planets' and put into a category along with Ceres and I think another asteroid, as well as one or two Kuiper belt objects.

-dh

Answer 6

It's the natural shape for objects in space to take on. You can see this by watching the astronauts play with water. The water naturally seeks a spherical shape. The gravity of the planets make a sphere the natural shape that they become.

Answer 7

Same reason as raindrops are spherical - the most stable shape because the sphere gives the highest volume/mass for the lowest surface area.

Answer 8

Because spherical shape has the lowest area with given volume.

Answer 9

Cohensive forces. Remember that before planets solidify they are a mass of liquid. In such case, surface tension (the attraction between the molecules of the liquid by various intermolecular forces) comes into play. Just like a drop of mercury.

Answer 10

because of the internal gravitational pull of the planet. It tends to keep the distance from its center roughly the same in all directions. Usually there is an eliptical or oblongness at the poles or axis of the orb.