In general, from a distance, you are correct that the planets are round. Gravitational forces gathered all the mass together and attracted it to a common center forming a ball. However, if you consider the height of the Himilaya's and Rockies and the depth of the ocean, you will see that on a more in depth view, the planet is less than a perfect sphere.

Planets are round because that is the most gravitationally stable shape. As an object grows bigger (aquires more mass), it generates more gravity. The mass of the body wants to be as close to the center of the planet as possible. The way to acheave this is to take on a round shape. So, as a planet grows and its gavity increases in strength, eventually the gravity overcomes the strength of the materials from which the body is made and pulls the body into a sphere. There may be localized deviations from a perfect sphere (mountains, valleys, etc.), but the overall shape for any object above a certain size will be a sphere.

it is beacuse of gravity i just learned that yesterday from Bill Nye lol :) Have a great Day!

Gravity

All of them except the newly formed ones which have not been rounded out due to the process of time.

As a body grows bigger, it acquires more mass. As it acquires more mass, it gravitational field grows stronger. Eventually, the gravitational field grows stronger than the materials from which the body is made. At this point gravity will pull the body into the most compact shape that it can. This shape is a sphere.

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. curious.astro.cornell.edu

Because if they were any other shape, people would be poking themselves on the corners all the time. ;-)

God has a gigantic emory board and smoothed out all the rough corners.

Gravity "smooshing" everything together to form a sphere. Tiny planets like asteroids don't have enough gravity to compact themselves into spherical shapes, that's why they look like boulders and potatoes.

The folks who have mentioned gravity are all perfectly correct. But let me put it very simply. Nature believes in compactness. For a given surface area, the sphere is the shape which provides the maximum volume. Put another way, for a given volume, the sphere is the shape which provides the minimum surface area.

are they

Don't question the work of the Lord.

They are square.

They are not round. or they all go around the sun.

Just a function of Gravity my friend, the sphere is the natural collection shape of anything with a collective force of gravity which then appears to act from the centre of the planet. The matter, if liquid, trys to fill in any gaps as it flows to the centre - A sphere. Even solids will redistribute, thats why there is a natural limit to the height of mountains on earth.

they are round because gravity pulls all the matter as close as it can. With the center of the gravitaional pull being in the center of the planet it would seem that it is all trying to get to the middle of earth

The planets are not perfectly round - they are 'squashed' at the poles. This is, I believe, due to the rotational forces acting against the gravitational forces. The earth's equitorial diameter (the distance around the middle of the earth) is 27 miles more than the polar diameter (the distance around the poles). This 'squashing' effect is even more noticeable in the gas giants, Saturn and Jupiter, and is quite noticeable in photographs.

Because of their own gravity. It has even been one criterion to define a planet: "The issue of a clear definition for "planet" came to a head in 2005 with the discovery of the trans-Neptunian object Eris, a body larger than the smallest then-accepted planet, Pluto. In its 2006 response, the International Astronomical Union (IAU), recognised by astronomers as the world body responsible for resolving issues of nomenclature, released its decision on the matter. This definition, which applies only to the Solar System, states that a planet is a body that orbits the Sun, is large enough for its own gravity to make it round, and has "cleared its neighbourhood" of smaller objects. Under this new definition, Pluto, along with the other trans-Neptunian objects, does not qualify as a planet. The IAU's decision has not resolved all controversies, and while many scientists have accepted the definition, some in the astronomical community have rejected it outright." "Since no overall consensus could be reached, the committee decided to put these three definitions to a wider vote at the IAU General Assembly meeting in Prague in August 2006, and on August 24, the IAU put a final draft to a vote, which combined elements from two of the three proposals. It essentially created a medial classification between "planet" and "rock" (or, in the new parlance, "small Solar System body"), called "dwarf planet" and placed Pluto in it, along with Ceres and Eris. The vote was passed, with 424 astronomers taking part in the ballot. “The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way: (1) A "planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. (2) A "dwarf planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite. (3) All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies"." "The IAU's definition mandates that planets be large enough for their own gravity to form them into a state of hydrostatic equilibrium; this means that they will reach a shape that is, if not spherical, then spheroidal. Up to a certain mass, an object can be irregular in shape, but beyond that point gravity begins to pull an object towards its own centre of mass until the object collapses into a sphere. Relaxing the demand for strict sphericity was mandated by the fact that many large objects in the Solar System, such as the planets Jupiter and Saturn, the moons Mimas, Enceladus and Miranda, and the dwarf planet Haumea, have been distorted into oblate or prolate spheroids by rapid rotation or tidal forces. However, there is no one point at which an object can be said to have reached hydrostatic equilibrium. As Soter noted in his article,"How are we to quantify the degree of roundness that distinguishes a planet? Does gravity dominate such a body if its shape deviates from a spheroid by 10 percent or by 1 percent? Nature provides no unoccupied gap between round and nonround shapes, so any boundary would be an arbitrary choice." Furthermore, the point at which an object's mass compresses it into a sphere varies depending on the chemical makeup of the object. Objects made of ices, such as Enceladus and Miranda, assume that state more easily than those made of rock, such as Vesta and Pallas. Heat energy, from gravitational collapse, impacts, tidal forces, or radioactive decay also factors into whether an object will be spherical or not; Saturn's icy moon Mimas is spheroidal, but Neptune's larger moon Proteus, which is similarly composed but colder because of its greater distance from the Sun, is irregular." Source and further information: http://en.wikipedia.org/wiki/Definition_of_planet Further information: http://en.wikipedia.org/wiki/IAU_definition_of_planet

Check it out: http://www.scientificamerican.com/article.cfm?id=why-are-planets-round&topicID=2

For rotation purposes.

I wish earth was flat, that way you could push your enemies off.

Any body that has sufficient mass will pull itself into a more-or-less spherical shape.

They are not perfect spheres (Earth is a little wider at the Equator for instance due to centrifugal force caused by rotating on an axis) The reason being is that the center of gravity exerts an equal amount of force in all directions, so cooling liquid rock will reflect the shape of the gravitational field in a spherical shape. +5

Because a universe of more-or-less spheres is much more elegant than a universe of triangles and romboids all trying to rotate at the proper speed to make things work.

due to the forces imposed upon them in their orbiting. Not exactly sherical, though.

gravity

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

Centrifugal force. The constant spinning of the planets determines their shape and size based upon how how quickly it spins and its overall mass...

The sphere (and it's one-dimensional equivalent; the circle) is a commonly-occuring shape in nature. All points on the surface of a sphere are equidistant from the centrepoint. A sphere is absolutely symmetrical in 3D. When a point expands outward equally it forms a sphere. A drop of liquid on a flat surface forms a circle. In space, a drop of liquid forms a sphere. A drop of oil in water forms a sphere. Air bubbles in water are spheres. A square-shaped stone when tumbled in water will eventually erode into a spherical pebble - more or less. I don't know if any of this actually has anything to do with why planets are round. Just thinking out loud ... :)

why do all humans have the same basic shape