Why are planets basically spherical in shape?

Answer 1

Believe it or not, they are all very squishy.
I know they dont seem that way, but at the size of a planet there just isnt a material that can hold its own weight, thier own gravity squashes them into a ball.

The earth....
Roughly 8,000 miles diameter, crust 18 miles, under that its liquid right down to an iron ball at the centre thats 1,500 miles across
so, the hard part is just a tiny layer on top of a liquid, gravity will do the rest.

Answer 2

Yes, Planets seem to be spheres, not cubes or cylinders or oddball rocky shapes. Some smaller bodies such as asteroids or Mars moons Phobos and Deimos, do have odd shapes, but larger bodies like the nine planets and most of their moons do look like spheres. That's because of the nature of gravity. You can think of gravity as a force that points inward toward the center of the planet so that every part of the surface is pulled evenly toward the center, resulting in a spherical shape.
Of course, planets are not perfect spheres because mountains and valleys and even skyscrapers are all deviations from the spherical shape. However, as planets get larger, gravity gets stronger, until eventually large objects on the surface are crushed under their own weight. That's why we don't have mountains that are 50 miles high or skyscrapers that are 2,000 stories tall. Planets stay basically spherical because any large deviations get crushed.

Although gravity keeps planets close to spherical, there are other forces that cause deviations from the basic spherical shape. For example, the rotation of the earth once every 24 hours, causes an apparent centrifugal force which creates a bulge at the equator. In fact the earth's diameter at the equator is 7,926 miles while the diameter between the poles is only 7,900.

source: http://www.pa.msu.edu/sciencet/ask_st/031198.html

Answer 3

Grace seems to be the only one who really answered this question in its entirety.

First, the planets, moons, stars and sun all appear spherical because the constant and equal gravitational force exerted on all sides of the bodies towards the center. However, in some cases, such as the Earth for example, there is a distinct bulge in places that change the gravitational perfect sphere into more of a squished sphere, or elliptical shape. This happens around the Equator because of the Earth's rotation. It can happen for other reasons, too, such as tidal effects like that of the Moon.

In no way is the spherical nature of bodies determined by their spin pulling mass inward as some have surmised. In fact, the spin actually pushes mass away from the center due to centrifugal force, again showing why there is a bulge at the Earth's Equator.

Answer 4

If you take a closer look you will both realize and recognize that everything constituting the entire Universe is "spherical" in shape and adopted by the same Laws. Think of the "Atom" which is the basic unit within a Molecule: it consists of "spherical" protons and neutron (except for the Hydrogen Atom which has no neutrons)...and "orbiting" the central core of the protons and neutrons are the "Electrons" which are also "spherical" in shape...as seen by the Electron Microscope. That is the same nature by which our "Solar System" functions: the "Planets", like the Electrons, are "orbiting" the Sun which constitutes the "neucleus" of the Solar System. All Stars within the Galaxy are also "spherical" in shape and all spin upon their axises at varying rates of speed. "Quazars" rotate at such enormous speeds that they send out "flashes" indicating their rates of axis spin which some have been measured to be many hundreds of times per "second". In the "Vacuum Of Space" any existing body that is "gaseous" (like the stars, our Sun [which is just another G-2 star] and planets like Jupiter), are spherical in shape because the "vacuum" of space is pulling upon the object from all directions with the same amount of force during the same moment in time. These are natural laws that I learned early-on in my career as a Professional Astronomer and is a truly interesting study of existing matter. You presented a good question which doesn't exceed good Common Sense like many I see on this web-site.

Answer 5

There is no such thing as gravitational pull. The planets are material flying through space in a straight line. The effect of gravity is caused by large objects distorting space-time. The sun is almost like a basketball sitting in the middle of a blanket being held up on all four sides. This dimpling of the blanket (space-time) means the straight path the Earth follows as its momentum through space takes it straight ... is a circle around the sun. As the material that formed the Earth joined together this curved surface smoothed it out and created the well-established sphere we see in all celestial objects. The sun in fact was subjected to this same process as it formed.

Answer 6

Planets (...and also stars) form within immense drifting clouds of gas and dust. Every bit of gas and dust generates a tiny gravitational force. In relatively dense regions of the drifting cloud (...called a 'nebula') two or more bits of gas or dust may be close enough so that they're attracted to each other by their gravity. They clump together, which increases their overall gravity. This larger clump is surrounded by more bits and pieces which are drawn in from all directions. The original clump grows in size and produces more gravity, which in turn pulls in even more material from all directions. The result is a growing sphere.

Answer 7

Gravity acts inward on all matter, focusing it in towards the center of its bulk mass. A sphere is the only shape that illustrates the concept of gravity acting with the same magnitude on all atoms of a planet.

Answer 8

gravity attracts matter inversely with distance.
Spherical bodies are the end result of the most efficient reflection of attractive energy.
ie
Spheres are the most efficient gravitationally bound shape, once enough mass is present.

the only non-spherical gravitationally bound objects are asteroids, whose mass is not enough to pull everything "neatly" into a sphere.

Answer 9

Because when they were formed they were gases so the surface tension made the gases have the smallest possible surface area i.e. made them a sphere.

Answer 10

When something is twirled around, it tends to assume a speriod shape